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've already found these two questions here, but none of the options given there seem to work.
I'm using Mac OS 10.8 and I've updated to the latest Minecraft release (1.6.4).
Best Answer
Most fullscreen programs on Mac OS 10.8 will use the four-finger swipe to switch between it and the desktop, but Minecraft doesn't obey this protocol. It appears to use a borderless window the size of the desktop instead of creating and using a separate fullscreen space. It also appears to set itself to be always on top, so Minecraft won't relinquish focus when you use ⌘+tab.
The only way I've found to quickly switch is, as you have, to turn off fullscreen. Fortunately, there is a faster way to do this: F11 is bound to the "toggle fullscreen" function. If you're using a laptop then F11 probably defaults to adjusting your volume or similar, and you'll need to use fn+F11 instead. The fn key is usually located in the bottom-left, under shift.