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.
I don't know exactly how knowledgeable I am, and I've only been on here a little while, but I try. I have a degree in Media and Communications, including what we call in Australia an 'honours' year, which was 2012. For my honours project, I wrote a thesis about the representation of nations in The Simpsons, so this year I watched the first 226 episodes (10 seasons) back to back, taking copious notes along the way. I hope to make some of the data available down the track. Over at my website, I have written a bit about The Simpsons, if you're interested. You can find it at http://www.travisholland.com.au/tag/the-simpsons.