I'm trying out OmniWeb these days. It has one amazing feature and several excellent features.
The amazing feature is workspaces. I loved tabbed browsing -- at first. Now I can't live without it, but it annoys me. On both Firefox and Mozilla I end up with a slew of windows, each with its own tabs. If I lose track of a tab, I wander through windows looking for it. In OmniWeb the Workspace gives me a hierarchical view of windows and tabs and lets me even rearrange the tabs between windows. I can display a mini-view of a tab to get more information than the tab title.
In the "just excellent" department I'd include their pop-up text editor for forms. Instead of making do with Blogger's textedit box, I have my own little editor. Slick and easy. It looks like OmniWeb has more than a few of these niceties.
Overall OmniWeb's rendering resembles Safari's -- they use the same web toolkit. Not quite as nice as Firefox and not recognized as Firefox by Blogger. On the other hand, OmniWeb doesn't suffer from the keystroke lag I get with Firefox on the Mac -- AND Mac services work with OW, they don't work with Firefox. Not to mention Firefox fonts and font spacing look pretty bad on my Mac.
Overall OW feels like a much better version of Safari. Worth paying for!