I know MattS has touched on this point before, but here's a pretty in-depth analysis of where various sluggers have sent their home runs.

http://baseballanalysts.com/archives/2009/04/alltime_home_ru.php

Howard has the third highest career percentage of his homers going to the opposite field, behind, of all people, Roberto Clemente and Julio Franco. It should be noted that neither hit as many home runs in their entire careers as Howard has already, and he's obviously far from done.

Also, Howard has the two highest (technically the highest and also tied for second) season totals of opposite field shots ('06 & '08).

Basically, I guess what this means is that he has disgusting raw power, and the only thing that prevents his flyballs from going out is if he doesn't get enough loft on them (especially to CF and RF). Not exactly earth-shattering to folks who watch him every day, but interesting nonetheless.