Well, I tried shooting my first high school baseball games this week. Having played the game for a number of years, I was able to anticipate some of the action....sometimes, I simply got lucky. I used a combination of 2 cameras (Canon Mark II and Canon 20D) and 3 lenses (70-200mm f2.8, 300mm f2.8 and 300mm f4). I also played with my 1.4x extender on a few shots as well. You can see all of the pictures on my Smugmug web site.
The biggest challenge with baseball is finding a location where you don't have to sit behind the fence.