Chrome has a nice "process viewer" built in so you can see exactly which tab is using how much CPU, Memory, and Bandwidth - it's a great tool for pointing your finger at a webpage and saying "ah-ha! YOU are hogging it all!".
IE always appears to be the least system-hoggy because of it's integration with Windows. Half the processes are hidden in Explorer and other rendering engines.
FF tends to consume a lot of memory because it likes to cache the last 15 pages you went to. When you have multiple tabs that stacks up pretty quick, but it is a convenient example.
Overall, though, I don't care. I have 1.5gbs and I figure if I can use it ALL, I should!
Only complaint about chrome I have is it's color scheme (which I've gotten used to, but skinning would be nice) and the mod community hasn't picked up their slack yet so there aren't a lot of plugins. Give it time!