I wish that I could say that I never do, but in reality I eat around my computer a lot more than I like to admit. The consequence of such activity is the inevitable crumbs and every other manner of food than ends up gumming up my keyboard and mouse. If you own the white Apple keyboard with the clear Lucite bottom, you know exactly what I'm talking about.
To prevent food and crud buildup in your peripherals check out the ProTouch line of skins from the folks at iSkin. Pictured above is their ProTouch for Mighty Mouse (US$20) in Sonic blue and the ProTouch FX (US$35) for Apple's aluminum keyboards. Both work with the USB and Bluetooth versions and come in several colors.
The keyboard skin takes a little getting used to and slows my typing down slightly so I usually remove it for long writing projects. However the iSkin for the MacBook Pro keyboards (US$30) is indespensible for protecting your notebook on road trips and at coffee shops. While iSkin doesn't market this, nor will they guarantee it, I'd bet that a notebook computer has a much better chance of surviving beverage-into-keyboard trauma with an iSkin than without one.