Give it a rest.
I know, I know - he's barely played above replacement level the last 2 years, is unlikely to get any better, and is surely going to take PAs that could have gone to younger players with more upside.
Obviously, one plate appearance does not a contract extension warrant...so let's cast the subjective anecdotal crap aside and look at the data...
According to FanGraphs - Schumaker actually earned his salary last season - here are his 4 seasons as a regular
2008: 2.6 WAR, worth $11.5M, paid 396k = $11.1M surplus value
2009: 1.8 WAR, worth $8M, 430k salary = $7.57M surplus value
2010: -0.2 WAR, worth $-1M, $2M salary = $3M deficit
2011: 0.6 WAR, worth $2.9M worth, $2.7M salary = $.2M surplus value
Clearly he's trending in the wrong direction and - given his age - is not a good bet to revert to peak form, but he's a decent bet to live up to this modest 1.5M salary in 2012 and 2013
Ah...but the opportunity cost of giving him the roster spot in the first place...
First, let's assume that Mike Matheny is a rational man who will give Descalso and Greene opportunities to win the 2nd base job. Schumaker represents the fallback if neither of those guys demonstrate they can hit well enough to play everyday. If it wasn't Schumaker, it would have been some other veteran infielder.
Also, he can play CF. We know he can play CF because he did it as recently as game 7 of the World Series. We THINK Beltran can still play CF, but the reality is that Allen Craig spent more time in CF than Beltran in 2011. Craig and Beltran each have knee issues and may break down - possibly at the same time. Skip Schumaker provides cover at CF. Again, if it wasn't Schumaker it would be someone else in the Darren Bragg mold.
Also, he can pinch hit. In the last 2 years, he's put up .375/.444/.417 in 27 pinch hitting opportunities. Other than switch hitting Berkman and Beltran on their off days, he's the best left-handed pinch hitting option on our bench.
So while everyone laments that he'll be irrationally be given too many PAs because that's how TLR rolled, the reality is that he's potentially filling 3 bench roles that aren't normally filled by a single player. He's a team player (fault the Cardinals for the 2nd base experiment all you want, but you cannot deny Skip has been a good soldier), and does not deserve the hate he receives.