Go to http://groups.google.com/ Start a new group Try and create a new Page "Page editing not supported in your web browser. Download a new copy of Firefox or Internet Explorer to edit pages." <rdar://problem/5889546> Google Groups: Page creation doesn't work
I encountered the same thing. In Safari 3.1.2 and a latest version of Webkit nightly build (528.2+)
The bug is fixed. I repeated above steps in the latest Webkit and I was able to create new page without any problem.