You can't see all 50-70 tabs on a normal 27" monitor; Chrome will squish them almost indefinitely, and Firefox forces a large minimum tab width that makes the tab bar scroll forever and then you forget half the tabs you have going and everything's bad. I tried to switch and stopped because of this. I'll hang on until ubo really stops working, I guess, and then try to figure something else out.
I can only speak to the comparison with hg, but for large repos, git's performance is literally 10x better in our case (we have two parallel copies, one in hg and one in git, so as to smooth the transition to git). hg seems more usable, but certain decisions are poor (e.g. baking the branch name into each commit); overall I have no strong preference between the two except for the speed.
But the speed pretty much drowns out any other signal.
Only those with the very wildest imaginations (which happened to include PG and the founders) realized that Airbnb was entering a huge lodging market. Most thought it was just dumb to think many people would want to stay in other people's apartments. See http://paulgraham.com/airbnb.html