'Made to make the Web a better place' it claims, so far I've only had to restart my computer twice in the three hours since I began running Firefox 4. Hopefully, this clunky heaviness will iron itself out with the inevitable upgrades, but thus far I'm less than ecstatic.
I'm really starting to hate upgrades too. They never seem to do anything good, and always seem to require more and more of this computers meager resources. I have a second computer, which is much bigger and more powerful and which I use for image work and graphics, but I keep that computer off the internet because I want to avoid all the detritus from using the internet (and because I wish to avoid the very sweet temptation of rejoining EVE online).