As inconsistent as Ubaldo Jimenez was last year (incredible 0.78 ERA in April/May last year; 5.16 in June/July; 3.25 in August/September) and has continued to be this year (5.86 ERA in April/May; 2.56 in June/July), acquiring a 27-year-old pitcher of his stuff who is under contract (through 2012) in return for a future designated hitter or first baseman is about as close to a no-brainer as you can come in the baseball business.
Adding: it may take more than Montero to consummate such a deal, but he should not be the impediment, nor should the spectacularly average Ivan Nova. Whether better prospects, the Bettances and Banueloses of the world, should be included depends on if the Yankees actually intend to use them at some point. That's a question you wouldn't ask of any team but this one, but it's a fair one given Yankees proclivities. Prospects are like produce-there is a "use by" date, after which they go moldy and lose whatever value they might have had.