gdgt

Well - it's kind of debatable. There's not a huge heat-removing effect from sticking a cooling pad on the bottom, because apart from heat from exhaust air, nothing else that generates heat is in contact with the bottom. A far bigger difference (and one you need if you are somewhere warm and need to do something even slightly strenuous with an MBP) is to waft cool air across the keyboard, not the base.

With that in mind, the consideration IMO comes down primarily to aesthetic aspects. The Balmuda X-Base is an option. (www.balmuda.com­/en­/products­/c­/x­-base/).

EDIT: I ought to stress that this advice is for the unibodies only. The pre-unibodies (i.e. up to mid-08) benefit from a contact / fan cooler on the bottom as they transmitted far more heat to the case, so they benefit more from air circulating under the machine as opposed to over.