I love Firefox and have been a user since... oh 0.7 or so? There's been great new extensions, improved stability, and new features except for a single nitpick- I've noticed that Firefox has become a really big memory hog.
This is After getting rid of memory leaking extensions and performing certain memory optimization tweaks. The best tip I've read recently? Get more memory. Ah well, more memory is good for my computer anyhow.
IE7? Well, I'll probably download it at one point when I have time to prevent it from taking over my entire computer. Probably not going to switch over just for tabbed browsing, though. I've got a lot invested in my firefox extensions and tabbed browser settings!