Yesterday, we saw the first public release of a radically new web browser for Mac OS X, the public beta of OmniWeb 5. On the surface, the OmniWeb interface remains familiar (more so than Opera), but now that the OmniGroup is relatively freed from writing their own HTML engine, they've been able to focus on the user interface.
Thus, there is now a real power user class web browser for Mac OS X. While Mozilla (and its smaller siblings Firebird and Camino) have long existed on the Mac platform, they've suffered from not being native. The Camino project was started as a way of addressing that issue by putting a native Cocoa wrapper around the Gecko engine, but the KHTML based Safari has taken most of its thunder away. (For a good overview of the choice of KHTML, read this message from the Safari engineering manager introducing himself to the KHTML community).
I'm not going to go into all of what makes OmniWeb 5 interesting. John Gruber has already gone into that, and quite well. The only point I disagree with John on is on bookmark management. Safari uses the same browser window to edit/use bookmarks. I like this feature. OmniWeb 5 allows for both the Safari Way and the "Separate Window Way." Granted, with window management systems such as Expose, finding bookmark windows is easier now than before. But I (personally) like knowing in which window and tab my bookmark will open, and Safari accomplishes this by keeping the bookmarks in the same tab as where you're browsing (you still have options to open bookmarks in new tabs and windows, etc).
Speaking of new browsers, yesterday also saw the release of Safari 1.2, which fixes some annoying problems from Safari 1.1 (particularly one which affected editing code in the Zope Management Interface), and has a long overdue "Save As..." option for downloading files and images to places besides the configured downloads folder. (OmniWeb still has this beat with their site by site preferences, which allow you to store downloads from vim.org in a different place than from VersionTracker). What makes Safari stand out is its engine. Yes, OmniWeb uses Safari's engine - but it's using an older version (for reasons spelled out in Gruber's article). Safari marches ahead with a fast OS X friendly CSS2 and beyond implementation.