Ballpark guess: 50. I have moved most of them to a private file but would have to do some digging to find just where that file is! :o
Right now there are 11 in my PM space, yet to be archived.
You have to give in order to receive.
Been contacted 5 times in 16 years, but two of them were in response to a thread in which I was whining that nobody ever PM’d me.
What am I? Chopped liver?
Makes sense. I’ve never sent a PM that was not a response to one I have received. Always believed that was intrusive. Yet here I am, expecting unsolicited PMs. I’m dumb.
I’ve been here almost 4 years–but I took a year-and-a-half sabbatical–and I have had to totally dump the main folder twice, so, 500+. Now, I do have a running gun battle with one of the posters on the other side of the US from me, but I like sending people notes, and jokes, and congrats and sundry crap.
You gotta send 'em to get 'em.
Let’s see, who’s next; oh, yeah, right…heh, heh… .
PM sent. 
139 messages received since 1999.
Biggest topic: various meetups
Second biggest: Feud threads back when Dolores Reborn was running those
Third biggest: prison questions
I’ve also sent 137 messages.
More than you could possibly imagine.
How sweet are you guys sending me unsolicited PMs. Not sure if they should be added to my official count, however.
As of right now I’ve got 844 PMs, dating back to 2007.
Going to have to start deleting some, soon.
As of right now I’m eliminating moderators from contention. Ya damn cheats!
If it helps, I had fifty two before I was made a moderator.
Several hundred times. A few dozen times a year.
Sixteen “first contacts”, discounting responses. Been here since March 1999 so slightly less than one a year.
Not too many, but I am super snarky, so… 
I have 109 messages sent to me, apparently. That’s way more than I would have expected, as I don’t feel I get any messages here. I guess that’s about 7 a year, and those probably comprise two conversations, so maybe that is about right.
About 2 per year.
47 in the past 15 years (oy!)
The bulk of them are with a fellow Doper who’d just moved to my area. At the time we didn’t have each other’s cell # so PMs were the easiest way to get in touch with each other.
I’ve also got a smattering of messages from different fellow Dopers re particular threads. Nothing bad whatsoever – contrary to the Pit, there’s a lot of support around here.
Nothing from a mod.
My PM limit is set at 500, including Inbox* and Sent Folder**. I presume mods get more space, so as to accommodate the large number of messages they routinely receive.
*current count: 191
**current count: 155
No idea why. Now I’m creeped out.