I have used WOT and have had great success with it.
David mentioned the precautionary issue about Script Redirects:
In all honesty these redirect google search results generally don't point directly at the site, but use a redirect script in the actual url string and WOT or McAfee, etc. won't make a blind bit of difference.
So, what needs to be done in order for Web Rep, WOT, or Site Advisor to make a difference in David's example? WOT has just released an update that allows for evaluation of shortened URL links on Facebook and Twitter, (It's out for Firefox and Chrome now, will be out for IE I think next month.)
Web Rep will get better if the following are added in a future update:
Implementation of ratings from virus lab data to co-exist with Avast community input.
Blocking of Red Sites by default (Like WOT already does.)
Jack