Got a lot of websites? Hopefully you don't have to monitor them all. That's because Google has limited the number of sites registered in Google Webmaster Tools to 500, according to Google Groups. Unfortunately, that number will not be lifted and you'd just have to get another account for additional monitoring if you're a regular John Doe.
However, if you're a partner, it's possible for the number to be raised, but it's a manual process, according to JohnMu. If you're affected, you can hop on over to Google Groups and ask for some help.
Forum discussion continues at Google Groups.
This post was written over this past weekend and was scheduled for publication on October 1st.