I'm pretty slow to catch on here, but it just occurred to me that tabs on top, like the Chrome browser has, are the best choice for people working on smaller (laptop) screens.
Usually I am working on a larger external monitor connected to my laptop. I never run the applications full-screen because the monitor has ample resolution. So then, the location of the tabs really don't matter mostly.
However, in the office they've introduced a "new way of working". Which means ditching all monitors, and have flexible work places. So I am now forced to work on my laptop screen. The screen has quite a bit of resolution: 1280x800. That's good in the horizontal area, but 800 pixels are too short vertically. The solution is to run everything fullscreen (hmm, DOS deja-vu) and use the screen as optimal as possible (auto-hiding start bar, no browser status bar, etc).
I'm a Safari person. I use it on my Mac all the time. Mainly because it is fast and I can sync my bookmarks. However, I didn't really get before what the fuss was about when those tabs moved around during the beta 4 period, but is starting to dawn on me now: Tabs on top are much more favorable than tabs "below". You won't notice this until you are using limited screen estate.
Look at the picture below. Both Chrome and Safari running fullscreen on my D630 laptop. Notice how much more content space you have with Chrome? And I think the title/tab bar and toolbar are quite bulky, so you can gain even more. That's not just a small gain, it is a huge increase!
Of course, if you see ChromeOS in this perspective, the tabs of Chrome being actual "task switchers" this all makes sense.
I'm still favoring Safari at the moment, because Chrome on Mac OS X does not yet have bookmark sync (don't start with comments like "use delicious" etc.. I won't). Once this is available, I may switch pretty quick. Unless Apple makes the tab position configurable in a new Safari drop. The old Safari 4 beta had a "tabs on top or not" tweak possibility but unfortunately this is gone in the final. I guess it's long forgotten now, but I was re-triggered by the attention chromeOS got and my personal experiences working on a vertical resolution challenged screen.