I've been playing around with Flock over the last couple days. It's billed as a "social web" browser with built-in integration and management of many popular online services. Since I have accounts with Blogger, Youtube, Livejournal, del.icio.us, and subscribe to many RSS feeds, I gave it a shot. I think it's a great browser with powerful features, but a little excessive for my current needs. Don't worry, Flock, it's not you, it's me.
Flock is a sleek-looking program and it fits a lot of resources into the screen real estate. An optional media bar across the top displays Flickr photostreams or videos from YouTube subscriptions. A versatile multifunction side panel can display summaries of RSS feeds, available web blogging/publishing/tagging services, starred items, favorite links, or the web clipboard. This universal clipboard feature was interesting: Just drag and drop text or images to the side and they'll stay there, presumably to help with research or blogging about the items saved. It seemed redundant with del.icio.us built in, and although it would be useful for compiling many items in one place, it doesn't log the URL or where they're from. Flock aims to be one-stop shopping for everyone's social online needs, even combining all the blogging services under one generic publishing window.
It's based on the Firefox architecture and claimed that many of the extensions would work, though I didn't try many. Twitter is not natively supported, but there's already a Twitterbar extension for it.
The drag and drop photo publishing and attaching functionality also worked well. However, I use Picasa and its Web Album feature, and I see no reason to migrate to Flickr yet.
Ultimately, I'm sticking with Firefox for two reasons: I don't use enough of the services offered by Flock, and I like the centralized control of my RSS feeds that Google Reader provides (tracking read items based on an online account and not a local, per-computer basis). If I used Flickr and only checked my RSS feeds from one computer, this would be perfect; for now, it's like buying myself an airplane ticket for a hundred-mile trip.