I regularly play Minecraft with a reference site, such as Minecraftwiki, open in a browser window. However, I haven't found an easy way to alt-tab between the game and a browser when the game is in full screen.
The fastest way I found yet is
Pause --> Options --> Video Settings --> Fullscreen off but this becomes cumbersome pretty fast.
I'm using Mac OS 10.8 and I've updated to the latest Minecraft release (1.6.4).