They use CMD-# for switching tabs. I think bookmarks are better because they're less likely to shift... but I guess its kind of handy if you always keep say gmail on your first tab.
Yeah, I think that a simple "left and right" to switch would work better. It's odd, though, how no browser has a really easy "shift tabs over" shortcut.
(you do know about ctrl-tab and ctrl-shift-tab right? Its pretty standard in tabbed windows apps, so I guess people just keep using it for consistencies sake.)