Banning Meebo sites in BorderManager can be a bit of a pain.
Here is a quick and easy way to block them in BorderManager using two rules.
New Rule > Action Deny > URL > Destination > Specified > Specify URL > http://*.meebo.com/* OK
New Rule > Action Deny > Application Proxy > Access Details > Proxy HTTP > Origin Server Port: 443 (leave "to" field blank) Destination > Specified > DNS Hostname > *.meebo.com > Add > OK
Disclaimer: As with everything else at NetIQ Cool Solutions, this content is definitely not supported by NetIQ, so Customer Support will not be able to help you if it has any adverse effect on your environment. It just worked for at least one person, and perhaps it will be useful for you too. Be sure to test in a non-production environment.