In an effort to help make this place a bit less of an, erm, carbon copy, I'm making a few suggestions to the effect of addressing that, hopefully in a good way.
Also, because it apparently confused people, you can no longer edit or delete pms from your outbox, sorry.
There is no limit as to the number of PMs here. After there are about a million pms in the system, people with thousands of pms (yes, I mean thousands) in their inbox will probably notice some lag when accessing pms. I suggest, if you are the hoarding type, that you begin organizing sooner rather than later.