Go to any story in Digg (the URL http://digg.com/world_news/Anonymous_responds_to_fake_news works as an example) and try to click a thumbs up or thumbs down icon. In Safari Version 3.0.4 (5523.10.6), the released Safari version, all works fine. In WebKit there is a slight pause, then a dialog appears saying "There was a problem completing your request. Please reload the page and try again.". Reloading has no effect.
*** Bug 17279 has been marked as a duplicate of this bug. ***
I cannot confirm this bug. Works fine here with Webkit r30119
This bug is not confirmed for me. Build: r30790.
Marked as WORKSFORME per comment #2 and comment #3. Ian, feel free to reopen the bug if the problem is still visible to you.