Prior to Safari, I was a die-hard OmniWeb 4 (then 4.5) user. I really liked OmniWeb, but Safari was much better (IMHO) at things like bookmark management.
I've been following OmniWeb's development, and really like some of the new stuff (using WebKit means pages render correctly, the new tab implementation looks pretty sweet, workspaces should be useful, RSS feeds(?) ...).
So, I'm going to try using OmniWeb 5 for a week, and see how it works in the field. I've switched my default browser to it so apps like NetNewsWire open it automatically. (btw, the tab thumbnails are awesome for opening stuff from NNW!). I'll post again in a week with some thoughts...