While I was riding to college today, I heard a loud bang (and I've heard a few of them since i bought the bike), and immediately thought I had busted a spoke. I was running a little late, and was almost to school, so I kept going.

Get to school, then when I'm finished, I head for home. As I'm shifting, I suddenly find myself with the chain stuck between the 5th and 7th cogs. I thought that something had expanded on the cassette, so I rode (downhill) to the nearest shop in the chain that I bought the bike from. They start looking at it, and realize that I'm completely missing the entire 6th cog.

Got the bike in June, so they warrantied the replacement..

So has anybody else had an entire gear go AWOL w/o crashing the bike?