What I found this evening in playing around with switchproxy is that there are a lot of really bad free proxies out there. I really don't understand why if someone was going to go to the time and trouble of running an open http proxy why they would use software that doesn't cull out user agent information, or worse, inserts the IP address of the originating host in the http headers!

(Upon further consideration I think what is going on here is that people are using proxies to bypass network layer net-nanny type services that filter by IP. As long as you update your proxy list faster then they update their block list, you can access any website.)

A lot of the services that provide proxy lists provide proxies of dubious value. Many that seem to rank proxies don't offer a nice text based output that can be fed into switchproxy. If anyone knows of a solid, filtered list of proxies please let me know.

This service will give you some decent information about how good your proxy really is.

proxyjudge.org - anonymity and security