I finally solved my Safari / Lion problems after a week of total difficulty. The Mac was unuseable even with 2 fresh system installs.
10.7.2 MacBook Pro 2.53 intel core 2 duo Safari 5.1.2.
Safari would lock up, spin beachball, crash, system hang, other apps e.g. mail & firefox would also freeze after safari was opened, only very long restarts would give brief (minutes) respite before the freezes restarted.
Twice I tried reinstalling Lion; booting from recovery disk, used disk utility to repair HD, repairing permissions, re installed safari, things just got worse every time I tried....
Now at last I think I have fixed it, by trashing all preference files mentioning Safari in the Library folder (option key & Go menu to reveal) and after crashing safari again, then restarting twice, I seem to have my old Mac back! Fingers crossed that things don't go awry again. I had previously trashed the prefs to no effect, but maybe I missed some that time...