It varies. My rain bike gets hammered on chains. I think I got 2000 miles on the last one, and should have replaced it in half that time.

Lube will also make some difference. Did you ride all summer without lubing the chain?

I've had some troubles with cassette and chainring wear from being late with chain replacement, so my new road bike gets them early (I think). I've kept the old chain, and may choose to put it back on, later if I choose to wear it down some more, but probably not.