OK, Flock is interesting. It really doesn’t seem to be much more than Firefox. It doesn’t have all the extensions you might want, but by editting the install file (really easy copy/paste job), all the ones i’ve wanted worked.
Bugs: gmail’s compose doesn’t work… that’s odd and annoying but not major.
Features: i’ve only cared about the integrated blog feature (what is doing this). It’s very useful. The favorites I have not checked out much. the search your history is very nice to save you looking for stuff again and again.
I think it has potential, but I need to figure out if it’s enough better than firefox to recommend people using it instead of firefox.