I've been doing play by post for just over 6 years now, I guess, as both player and GM. My gaming group left town just after college and none of the other groups I tried were ever a good fit for me. After years of getting together once or twice a year, we found PbP and love it!
Pluses are that you have time to think about your actions and the non-face-to-face nature tends to free people up to role-play a little more. Minuses are the pace (though this doesn't bother me at all any more) and the fact that it's much harder to convey tone accurately on the boards - which sometimes leads to misunderstandings.
This is the first scenario Vig's been through - I've got one other active PFS character who's in his second scenario.