I'm not trying to defend Guzman but a lot of you guys seem to think Hudson isn't really much of a defensive upgrade over Guzman at any position, while attributing a lot of value to his bat. But is that really fair?
Guz had 74 runs and 52 RBIs in 135 games.
Hudson had 74 runs and 62 RBIs in 149 games.
Guz had 41 runs in the first half, 33 in the second
Hudson had 53 runs in the first half, 21 in the second
Guz had 24 RBIs in the first half, 28 in the second
Hudson had 48 RBIs in the first half, 14 in the second
And so on and so forth...
I'm not saying Guz is better or even equal, or that I necessarily want to see another full season of him, but I question how much of an offensive difference signing Hudson really makes, especially when we're already on the hook for Guzman's salary and most seem to want Desmond to play.
Guzman had 20 errors in 117 games in 2009. Hudson had 8 in 145 games 
Am I imagining things or haven't I been watching most of you talk about Hudson's superior offense and questionably better glove? Five minutes of looking at the stats would seem to indicate the exact opposite to me, at least on the face of it.
My counter argument:
Guzman wOBA - .301!!!! (that's pitiful)
Hudson wOBA - .342 (above league average, not by a lot though)
Guz wRC (runs created from wOBA) - 54.0
Hudson wRC - 82.7
and the important one for hitting here
Guz wRAA - -12.5
Hudson wRAA - 5.9
Guzman was considerably below average in producing runs... the average MLB (not replacement!) player provided 12.5 more runs than Guzman over the course of a season. Hudson was above average, not outstanding, but solid.
Now on to fielding.
Guz - -2.6 UZR/150 last year vs. -0.8 over career
Hudson - -3.7 UZR/150 last year vs. 2.6 over career
Numbers say Guz had a better year last year, Hudson has had a better career. Overall, both were below average, with Guzman performing better according to UZR.
Now on to WAR (the accumulation of batting and fielding):
Guzman WAR - 0.9
Hudson WAR - 2.9
Hudson is worth approximately 2 more wins that Guzman. A few notes here... Guzman got a positional adjustment of 7.5 vs. Hudson's of 2.5, an assessment I disagree with (IMO there are better hitting shortstops than second basemen overall, or at least equal). In any case, Hudson's RAR was about 20 runs more than Guzman's.