I recently needed 256MB more memory, having only 512MB. I could put a new memory stick in my laptop (this is a problem because either it's 2 256MB cards, or it might short out, as it did when I tried to upgrade the RAM months ago). My solution? Well, Firefox was using 350MB to display 10 tabs. I upgraded Opera to 9.64, put those links in 10 tabs, and it uses only 150MB. So I've saved 200MB without upgrading my RAM!
Yes. I have 5 windows with a total of maybe 180 tabs, using about 800MB.