Taking a cue from this article on Indians GM Mark Shapiro, here is my take on Kenny Williams' five best and five worst moves during his tenure as GM. They are in chronological order.
Hits
November 30, 2000 - Re-signed Jose Valentin to a 4 year/ $20M contract.
Would it surprise you that Valentin is the 376th most valuable position player in baseball history? Coming off a spectacular 5 WAR season in 2000, Williams locked up Valentin for four more seasons. And, while not reaching the heights of that season, he provided 2.9, 3.2, 4.2 and 2.9 WAR over the contract - production worth approximately $35M. Valentin remains one of the more underappreciated players in recent White Sox history.
December 11, 2003 - Signed Mark Buehrle to a 3 year/ $18M contract extension (with $9.5M 2007 club option)
I don't think I need to cite any numbers for this one. He's quite simply been one of the most valuable pitchers in baseball over the course of his career. While he's consistently been underappreciated by projection systems - in part because of his own defensive prowess and in part because of his unique repertoire - his performance has not gone underappreciated by White Sox fans. Even including the 2006 hiccup, Buehrle was paid less than half his value over the contract.
December 17, 2004 - Claimed Bobby Jenks off waivers
When you acquire one of the better closers of the last five years for a waiver claim fee, it's going to be a hit. However you want to value closers and however you feel about his current salary - and there is plenty of debate over both - there is no debating that Jenks has been excellent ever since he was called upon late in the 2005 season to take over as closer.
March 20, 2006 - Traded Joe Borchard for Matt Thornton
Quite simply, this was highway robbery. The bustiness of Borchard need not be elaborated here since it was done here. Thornton himself was considered a bust by Seattle. While panned at the time, it reputedly took Don Cooper only a single side session to make a slight modification in Thornton's delivery (lengthening his stride) and curing him of his inability to find the strike zone. The rest is history. Thornton has become the premier set-up man in baseball over the last four seasons and is signed to perhaps one of the most ridiculously team friendly contracts.
December 6, 2006 - Traded Freddy Garcia for Gavin Floyd and Gio Gonzalez
White Sox fans universally noted the devolution of Garcia into a junkballer during the 2006 season, with across the board velocity drops. Despite this, and Williams' reputation as a guy who trades injured pitchers (thanks Mike Sirotka!), the Phillies decided to take Freddy and his $10M salary for 2007 off the White Sox' hands and send a prospect who was considered a bust back to the White Sox, along with the highly-rated Gonzalez (who had been sent to Philly by the White Sox the prior offseason for Jim Thome). Predictably, Garcia pitched only 58 awful innings before having season-ending shoulder surgery. Floyd spent the 2007 season largely in the minors but in 2008 had a breakout season. And despite the poo-pooing of many in the sabermetric community, who spent a bit too much time with their noses in the numbers and not enough watching the game, Floyd solidified his status with an excellent 2009 season.
Misses
December 13, 2001 - Traded Kip Wells, Sean Lowe and Josh Fogg for Todd Ritchie and Lee Evans
After three solid seasons for the Pirates, the White Sox traded two young, well-regarded pitchers in Wells and Fogg for Ritchie, who was simply awful in his one season with the club. While this trade does not look nearly as bad to me in hindsight as it did at the time, it did show the inability of Williams early in his tenure to realize the value of cost-controlled players. Wells never was much more than an average innings-eater type but he alone was far more useful and valuable than Ritchie was in his one year here.
April 12, 2006 - Signed Jose Contreras to a 3 year/ $29M extension
FIP proponents are probably going to argue this one. They'll point to Fangraphs' valuation and say he was worth his contract. The problem with that logic is that it neutralizes one of the things that Contreras is just terrible at - having runners on base. If you're not using a walker, a single or walk may as well be a double. There are other issues, which are elaborated on here. Suffice to say, Williams didn't envision the guy producing an ERA of 5.00 and facing multiple injury issues when the extension was signed. This perhaps shows the danger of signing an older player to an extension almost a full season before he hits free agency (although a similar move with A.J. Pierzynski panned out).
November 23, 2007 - Signed Scott Linebrink to a 4 year/ $19M contract
Last offseason, I evaluated this as the worst current White Sox contract. It looked bad when it was signed and nothing has changed. He's been basically useless. And there's still two years left. Why Williams broke from his usual M.O. and signed a pitcher for four years is a mystery.
January 3, 3008 - Traded Ryan Sweeney, Gio Gonzalez and Fautino De Los Santos for Nick Swisher
November 13, 2008 - Traded Nick Swisher and Kanekoa Texeira for Wilson Betemit, Jhonny Nunez and Jeff Marquez
May as well handle these together. The initial trade elicited generally positive reactions - a player signed to an undermarket contract who had provided about 4 WAR in each of the prior two seasons and who was about to enter his prime is usually a good thing. Sure, the price was high - De Los Santos and Gonzalez were probably the top talents in the system and Sweeney looked like at least a 4th outfielder - but the return was solid. Then Swisher had a very subpar season in terms of production (for reasons largely of luck), apparently pissed off management and other players and was summarily shipped out for garbage. At which time he promptly returned, as expected, to his prior level of 4 WAR production. Whether you think Swisher deserved to be traded away rather misses the point because, if you think that, he shouldn't have been traded for in the first place. As discussed previously both here and elsewhere, this was a ham-fisted job of player evaluation the whole way through.
The Take Away
It was a lot harder to find misses than hits. This is a function of a multitude of factors. First, Williams rarely signs players to contracts longer than 3 years. Second, as re-confirmed recently, the White Sox are superb at preventing playing time lost to injury - which is usually the primary cause for a contract or trade to go horribly awry. Finally, the White Sox are good at evaluating their own prospect talent and tend to trade them at the height of value.
As I'm sure you noticed, this was generally a results-based analysis, which I think is completely fair for a decade-long tenure as "luck" should be balanced out and skill should show through. As such, there are some recent transactions which need more time. Chris Carter for Carlos Quentin could end up looking pretty bad if Carter, ranked one of the top prospects in baseball, pans out and '09 Quentin is the real version. The John Danks trade was a late cut, which again speaks more to Williams' abilities than anything. Alexei Ramirez probably only needs another season to go from "very good" to "coup" level. The Alex Rios waiver claim could be a miss, if only because long-term deals like that are rarely favorable. And if you're of the type to include draft picks, there's this Beckham fellow who may be okay.
Add your own lists below. A good tool is this spreadsheet of transactions, though it is only updated through the 2008 season and has some notable absences. See also here.
*Note that I used Rally's WAR database for this post because it goes back prior to 2002.