Yep, although from what I recall they're actually not biodegrable at all and are in fact rather hardy - still, best to leave something for future civilisations / aliens to excavate and ponder over.

I think the thing is that they're small. Also, it's perhaps preferable to stamp one out in the street to be sure that it's not going to set fire to something - I used to prefer to not chuck the things in trash cans.

Ha, I've just remembered being out for a drive when the smoker in the car in front chucked her fag out of the window but it didn't make it outside. Unfortunately she was a horsey type and had bales of hay in the back of the car. The consequences were soemwhat inevitable.