Google chat can be blocked, without blocking google.com on the whole.You must block chatenabled.mail.google.com with the ports 443 and 80 to talk.google.com.Linux users can use iptables to redirect the traffic to 127.0.0.1 (your local loopback address) You can also use the old fashioned /etc/hosts for the same...

I had to write this post here, because there's been a lot of attention to blocking google's chat lately.

Cheers :)
Kish