I really, really like it. I've been collecting a small armada of web apps using Mozilla Prism (which was nice), but this basically has the same feature built-in, and much faster, too.
Additionally, I have 2 main Firefox profiles I use - one (Personal) with personal bookmarks and fun extensions, and another (Work) with clientelle bookmarks and web dev extensions. Both those profiles load relatively slowly. My default web browser, when a URL shortut is opened, has been another Firefox profile, this one without hardly any extensions, and with no history tracking, cookie saving, etc - a guest browser, if you will. It's been fine for that purpose, but Google Chrome has just replaced it as my computer's default browser.
Only major nitpick I have so far is that
GridMove - a mandatory app for anyone with a large monitor - doesn't seem to pick up on Chrome being a window. :-/