This is an OK trade for the Yankees. Granderson will out-produce Damon at a cheaper price so that is a plus. He will also be playing in a LHH park so that is a plus. He makes the OF defense very good with Melky and Swish/Gardner/OF to be named later.
The down side is he has very poor plate discipline. His doubles, triples and average have dropped precipitously as he has become a flyball hitter, opposed to a line drive hitter. He won't be facing AL Central pitching on a regular basis, but rather some of the better staffs in the AL in Boston, Tampa and Toronto (if healthy). He is also abysmal against LHP so he may require a platoon (Nady?).
That said he is still a top notch player and will probably be better than worse in pinstripes.
If I was a Yanks fan I would be concerned about the opportunity cost. This takes them out of the running to trade for a pitcher. Without Jackson and Kennedy they are down to Montero/Hughes/Joba if they want to trade for a marque pitcher. This means they either start Phil and Joba at 4/5, go for a rehab project (we know this doesn't always work) or go the FA route and get Lackey.
So IMO they get marginally better this year, save some money, drive the cost of Halladay (as they most likely won't be suitors - can't see why they'd trade Joba+ or Hughes+ for Halladay when they wouldn't for Santana), Holliday and Josh Johnson down.
I think this bodes well for the Sox's if they are trying to pursue a trade or Holliday.