Flock web browser is dying as of April 26, 2011. I know David Warlick has always loved it.
Although the official Flock page recommends Google Chrome or Firefox (IE is strangely absent) - I recommend Rockmelt instead and I've reviewed this before. I use RockMelt when I feel like being a social surfer. I use Firefox for power browsing and Chrome when I need speed!
View of Rockmelt Browser from the Review I did in December about this cool social web browser