Ask most American League hitters and they'll tell you: It takes a well-struck baseball to leave Angel Stadium. Pitchers generally love it. The Angels rarely play day games and the Pacific Ocean helps keep things cool at night, so conditions combine with deep dimensions to make it fair, but slightly skewed in the pitchers' favor.
And yet, according to some, Albert Pujols could actually gain by switching ballparks. Busch Stadium negated much of Pujols' power to right-center, costing him home runs. He hit 37 last year and, in the above link, it's conjectured that he might have hit as many as 16 more if Angel Stadium were his home park. Especially in day games, the right-center power alley is one of the few areas of Angel Stadium susceptible to home runs. Mike Napoli likes to hit them over that scoreboard.
Hard to believe that Angel Stadium could actually help a hitter, but maybe it'll be good for a small spike?
According to ESPN's Park Factors under the "Resources" tab, Busch Stadium was one of only five major-league stadiums where it was harder to hit a home run than Angel Stadium. Of course, these things are dicey. For one thing, the Angels had the advantage of playing about 20 games at home against the weak-hitting Seattle Mariners and Oakland A's. They also had the advantage of being able to use Jered Weaver, Dan Haren and the rest of their well-above-average pitching staff. So, maybe it will be worth even more to Pujols to get out of Busch.
Changing stadiums: Yet one more reason to be excited to see what Pujols does this year.