We've covered Flock before, but just in case you didn't catch our previous posts, here's a quick rundown: Flock is an OS X/Linux/Windows open source "social web browser" built on the Firefox core, offering various well-integrated tools for contributing back to the web you're browsing. Amongst other things, it has a built-in blogging tool, bookmarks are saved to online sharing services (del.icio.us, and now Shadows), Flickr surfing/uploading and a whole lot more.
I bring this all back up because I just noticed that Flock has updated their developer preview to version 0.60, with a lot of additions and improvements: drag and drop Flickr uploading, searching Flickr by tags and text, a new blog editing engine with support for categories in WordPress and other MovableType-based blogs, the shelf can act as a topbar, a new online bookmark service (Shadows.com) with support for private online favorites (del.icio.us doesn't do that), a Technorati topbar, a better RSS reader and more.
While Flock is still a developer preview - which really means pre-beta - I recommend you still give it a look. I heard a podcast interview with one of their higher-ups who didn't recommend anyone pick it up as their main browser, but they still do a good number of things that either haven't been done in other browsers, or simply aren't done nearly as well through plugins and extensions.
You can download the developer preview here, as well as a full list of release notes and changes here.
[UPDATE: I'm not sure what's up with the Flock download page, but version 0.60 is apparently not available for download (the links point to the previous 0.4.10 version). TUAW reader Joel noted in the comments that the most recent version, 0.5.10, is available from the hourly builds page.]