The recent spam wave was 10 pages, with multiple accounts posting multiple spam messages. I had thought that limiting a new account to 5 posts would help, but I realize that approach will just make the spammers create more new accounts. It's probably easier for the LTB admins to delete 5 spam accounts with 50 spam messages each rather than deleting 50 spam accounts with 5 spam messages each.
I think Adam's idea of pay-to-post is the only way to fight this. There has to be a cost to the spammer in order to prevent spam. Right now, it only costs the spammer some time, and they seem to have plenty of that.
Edit: I reported at least one spam message from each spam account I found in the 10 pages of spam.