Ok so i had a customer that wanted to block iGoogle but allow google which turns out to be tricky as the only way to tell the difference is by the gadgets and the title bar.
i tried to do some research about iGoogle: every sites of iGoogle what I tested has the same title in html source code. Exactly:
So you can use DLP sensor to detect this title in http request and block this sites. I have tested this on a FortiGate-60B with 4.2.3 version of firmware.