Safari/Webkit networking hangs.

I am experiencing a recurring problem with Safari. It gets into a state, where no site can be visited. the progress bar moves about 20% of it's distance and just gets no farther. I can leave it for many minutes. Firefox and Chrome continue to work fine. Manual tests of network services (ping, nslookup) work just fine. The only solution I've found is a hard power down and reboot. I try to just do a Restart, but I end up with a windowless Mac desktop, and it never shuts down.

When it comes back up, Safari works fine, for a while. I'm probably averaging 1-2 restarts a day.

I've tried my best to cleanup Safari. Disabled all extensions. No improvement. Other suggestions?

(I included Webkit in the subject, because I think I've seen similar problems for the Mail.app once it has gotten jammed up).