I just decided to clear out the over 1000 spam messages in my spam filter box - it shrunk my mailbox by 20 megs.
There's way too much spam now - around one sixth of my mail is spam. Just as I deleted the last message from my spam box another one arrived.
On a related note, my ISP had to shut down their mail servers for half an hour this morning because 26 customers has virus-infected PCs sending out 30000 messages over 8 hours - that's 3750 messages per hour, which is 1.04 messages a second, along with all the real mail that had to be sent.
Some people just like to ruin it for everyone...