I've been curious about this for sometime. Does anyone know how many episodes of Seinfeld Jerry Seinfeld personally wrote or co-wrote? Every once in a while his name pops up when I'm watching a rerun as having written the episode. but if you go to IMDB he's listed as creator and therefore listed a "writer" for every episode.

He really didn't write a ton of them over the years. I'm sure he had input on a lot of them even if he isn't credited as writing.
http://en.wikipedia.org/wiki/List_of_Seinfeld_episodes

What about the short monologue at the beginning of the show? Could one assume he wrote that part of the show?

Wasn't it the norm that the writers would submit their draft to Jerry and Larry, then they would have a all night rewrite session making it more seinfeldian?

Yep. In the retrospective DVD that's included in the Complete Series boxset, they discuss the writing process. This is pretty much how it went during the whole series until David left.