The limit is found pretty soon on older machines; while the OP tests on a Mac with 8GB of Ram, on my main machine I have only 2GB of Ram, and Chrome becomes unresponsive after ~10 tabs opened.
I didn't think Firefox would be better but if it is, I might go back to it!
I have 1.5GB of RAM and I usually have ~15-20 tabs open without any performance hits on chrome, (including Eclipse, Skype, filezilla calc, evernote etc etc open). Maybe there's something wrong with your install?
I have 6GiB of RAM, and Chromium eats most (typically, about 70-80%) of it. When I have too many tabs open with a lot of browsing history (for reference, currently, I have 61 tab open) Chromium eats all available memory, so, obviously, system chokes on swap.
Still, I prefer manual memory usage control (I have a meter in my panel, near the clock). This feels easier than less-predictable browser-wide hangs where I can't even switch the tab. I've tried Firefox 4 when it was released and I was unsatisfied with its responsiveness, for example, when I open a lot of flash-heavy tabs. While I've heard Mozilla devs did move plugins to separate process, in practice there were cases that the browser did hung for several seconds.
I didn't think Firefox would be better but if it is, I might go back to it!