I just downloaded the public beta of the Flock browser for Mac OS X.

I'm quite impressed. It's based entirely off the Firefox code base, so a lot will be familiar to Firefox users. The Flock developers have drastically revamped the interface, and socialized it as well.  Adding and sharing bookmarks, blogging (this post was published through Flock), rss feeds organization and viewing— all have been integrated into the browsing experience.

I'm particularly impressed with the integration of Flickr and del.icio.us. I won't bother describing what is best experienced by downloading the thing.