Right now I am in FireFox, but that is mostly because of comfort. I am slowly figuring out how to configure Flock to where it is as useful as I have learned to make FireFox over the years, and then I will switch over completely. While the services that are built in don't include most of my current favorites, the addition of functional plugins from FireFox addresses that issue. The browser is young, so I expect themes to exist to change the interface and get those tabs out of my way soon. Overall, as a social media addict who works on the internet, this browser is almost perfect for me, and as soon as I can hack it to act the way I like it, it will be my browser of choice.
Final Word: If you like social media and FireFox, Flock is for you, but you might want to wait until some themes are out for it.
Looking for the best FireFox add-ons and plug-ins, read FireFox 3 Extensions Roundup