More than 1000.
And thanks to Fusetalk's continued idiocy, it does NOT tell me how many PMs I have from each particular user - instead, it tells me how many PMs that user has, which is of course utterly useless.
Oh, and I can't see the first message from each person, and therefore can't delete the message, which of course means that said persons' usernames continue to appear on my list, making it that much more difficult to prune out unwanted messages.
Fusetalk: Y'all can really be a bunch of morans sometimes.
Oh, and I did once try using the Export feature, long ago.
The wonderful formatting of the plain text file was more reminiscent of the aftermath of a dictionary + C4.