Greetings All:
Oooook, this isn't a major feature, but I think it will be helpful.
It was inspired by this thread that was started by VictorKaum.
If your PM box fills up, you'll now get a little pop-up message while surfing the site attesting to that fact. You can then go to your PM Box, and delete or download messages.
You can optionally choose to turn on/off this feature under your Edit Site Options page. By default, this option is turned ON.
Enjoy!