I'd rather see the Yankees trade for a top-tier pitcher (Santana) than for a top-tier hitter (Cabrera). I'm only willing to trade one of the Trinity to acquire either.
Joba has the hype to be the centerpiece of a trade. While his potential matches that hype, his performance will not catch up for several years.
After pitching 112.1 innings in 2007, we can only count on him for about 140 innings in 2008, which means about 170 innings in 2009, and finally 200 innings in 2010.
Both Hughes and Kennedy are prepared to pitch 180 innings in 2008. That makes them more valuable than Joba.
In considering what is best for the Yankees in 2008, the only logical conclusion is to trade Joba Chamberlain for a pitcher capable of 200 innings while holding onto Hughes and Kennedy.