that took me a while to write, so the answer is not that often. also, i moved back to canada (i'm on a layover in minneapolis right now) and took only seasons 7, 8 and 9 with me. if i started one, it would have to be from those three seasons. much apu about nothing has already been covered in a very old thread.
this doesn't mean you can't start one though. in fact i'd encourage it! that'd be awesome.