I rarely post anymore, but I have enough old content in popular tags to gain close to 1k a month through random upvotes (that's about three votes per day).
I get a little 'interest' too, about 300 - 500 monthly.
Its the same on most sites, my rep has stalled mostly after becoming a moderator on Super User and its the same for most of the others there.
However, it doesn't mean that the sites stop being useful, I read a lot of questions, but rarely feel the need to ask a new one.
Man, tell me about it. I was in the top 10 when I became a mod, now I'm on page 3.
btw, this is Bill. :)
Because the mods haven't all looked at your email addy already and figured it out? =)
I'm trying to post, as I want to keep my MVP award (free MSDN subscription, what), but yeah, moderation sucks not just the time, but the will to put something back into the system sometimes.