Michael "Mendoza" Martinez is not a good baseball player and if he ends up getting a lot of at bats in 2012, that means something has gone seriously wrong.
That said, there was a 25 game stretch last season during which Martinez hit .279/.333/.441 with a BABIP of just .315. But even with that "hot streak," he finished the season at .196/.252/.282 in 234 plate appearances. His BABIP on the season was .220, so maybe there is room for improvement. Plus, as Wilson Valdez's tenure here illustrated, a player who can field multiple positions competently can be at least a little bit useful. Most projections seem to think he will OPS between .600 and .640, which is basically what Valdez would have gotten you anyways.
That's all. It's impossible for me to justify to myself writing more than 150 words on this subject.