Like he said, Flock has a lot of potential, its a tad slow right now and could use a better RSS reader a la mode de Firefox. Thats my only complaint, that and its a RAM hog for a lot of tabs, a few it manages well, but a lot it doesn't. But indexable history is a god send. I don't blog, so most of the features are.... well... but the history is great for research.
I use Safari and switch to Flock for research. I mean its good, but I just need a bit more speed. I find Safari a RAM hog though. Hopefully if Flock gets a bit faster, and a bit better tab management, and RSS. It'll be the premier app.
Other features I like.... Shiiras expose for tabs... great
Safari's private browsing (there is an extension in Flock, so i guest i has it.)
I forget which, but search choice by justing putting a letter in front of ur search... like G for google
Weather in the status bar.... flock again
Not only left and right movement for tabs but 1,2,3,4.... Flock...again
Flock developers... make quick process and you will be reeling in the dough, you will leave everyone in ur dust.