I've posted some screenshots of Flock 0.4.9 in the gallery if anyone is interested. It is said to be based upon Mozilla and it's quite evident by looking. Althought I have noticed a few additional features and a really cool theme (icons, progress bar, etc), it basically looks like firefox.
There's that cool "star" feature which appears to be a one click bookmarking tool. It has a choice of search engins in the toolbar, chosen from a dropdown list. It has a rssview, that shows what a rss supported site looks like perhaps as a rss feed. I noticed flickr and del.ico.us extentions in the configuration. Some other early extentions include enhanced google search and adblock (although instead of installing it, it downloaded and rendered the code in a broswer window). One of the nicest features is the "Create a blog post " option. From there one enters their url and the post, and Flock will upload it. However it won't work on Tuxmachines because I disabled that option for security reasons. The fonts look good as well.
I've not been using it too long, but it seems stable so far. I uploaded those screenshots with it and I am now posting with it as well. These are usually pretty good tests for a browser. So, although to me it looks like a mozilla/firefox clone, I've read there's quite a bit of original work under the hood. All in all, it seems fairly neato at this point.
Screenshots  in the gallery.