It had nothing to do with the server move - the exact same files were copied form one server to another, not re-installed.
The Vbulletin forums alude to an issue with some ISP's who use dynamic IP addresses. Something in the polls feature is incompatible with the way some ISP's change your connection IP during a session. Users who are assigned a single IP address during the whole time they are connected don't seem to have this issue.
AOL does change your connection, and often. I've no doubt that some other ISP's do as well. If you'd like to test it out, every 10 minutes or so, go to this page and reload. Record the IP addresses you get.
http://amitymama.com/cgi-bin/ip.pl