OK, I know I said I'd upgrade to IE7 later, but I seriously couldn't resist the temptation -- especially since I have nothing to lose by upgrading now; IE is not my default browser and I'm not using anything that might not be ready for the upgrade. So how am I finding it?
Internet Explorer 7 feels much better than 6. Tab support is awesome, and rather faster than it was before, although still not as fast as Firefox's. And the keyboard shortcuts for switching among tabs should definitely be simpler than Ctrl-Tab and Ctrl-Shift-Tab -- they should really be Ctrl-PgDown and Ctrl-PgUp like they are in Firefox. That said, I've just discovered the Quick Tabs feature (shortcut: Ctrl-Q), which may just be the best tab-related feature I've seen yet in a browser. Press the key and IE shows a tab containing thumbnail previews of each of your tabs, and you can go to the tab you want with a single click. This is amazingly fast, and really cool.
Everything else they've done, including getting rid of the menu bar and putting the the address bar right below the title bar along with the navigation buttons, I applaud because it just increases the screen viewing space in the browser. Who uses the menus in their browser all that much, anyway? And if you need it, you can just right-click on any toolbar and turn it on. Or just press the Alt key to turn it on temporarily.
IE still doesn't have extension manager as convenient as the one in Firefox, but that's OK, I've invested a lot in Firefox, including future plans with Greasemonkey; and I wouldn't really switch back to IE even if it had awesome extensions. (Well, maybe if they had a Greasemonkey-compatible extension....)
So to conclude? IE7 feels like a hit. Definitely go for it. But as for Firefox 2? I've dowloaded the installer, but I'll still wait out the couple of weeks to get it through Mozilla's updating channels once they've made sure all the best extensions are compatible with it.