It failed Google my compatibility test. When I pasted text into the Blogger BlogThis! window it rendered outside the window borders.
This is also true of Safari 3, and since I know there are of text pasting issues with S3 and Google's various products I didn't bother with any further Google testing.
On the other hand PPC performance is noticeably better than FF, which is slow in every way (especially keystroke processing). It's comparable to S3 or Camino.
I won't use Safari 4 any more than S3 -- I really need Google compatibility.