Great topic! I currently have 464. And, this is after a big effort on my part to weed them down since I know Phillip has been wanting us to reduce our numbers of PMs saved. Recently, I was up around 600.
I still have the very first PMs I ever received here at BetterMost. I'm very sentimental about them.
I also wish there was a way to count the numbers of messages in the PM outbox. I know I have more of those than in my inbox at the moment.