I grabbed a beta of OmniWeb 5.5 the other day.  A few days later is has replaced Opera 9 as my default browser on OSX.  Why?

• It’s super fast.  My main complaint on OmniWeb 5 was that it was slow.  5.5 beats out Opera and Safari quite easily.
• I can use Emacs keystrokes in it, just like the rest of OSX.  I couldn’t do that in Opera (Opera has a load of it’s own keystrokes and they seem to interfer with each other).
• The tab drawer.  Really.  It’s very, very nice.
• I love having configs per website.  On one site, I may need popups, but on the other I don’t ever want to see them.  OmniWeb makes this extremely simple.
• I actually had a problem with logging into a site (i.e. it wouldn’t log me in).  I filled out a feedback email, and got a nice automated reply stating that someone will get back to me in the next business day.  Sure enough, a real-live QA guy emailed me back and was quite nice.  I sent a trace back and he told me the issue is known.  This kind of support encourages me to by OmniWeb 5.5 when it comes out of beta.
• I just feel more productive in it.

So, really, give OmniWeb 5.5 a try.