Okay, this is picky, but as a use-case scenario I claim that I have a valid point, dammit.
In Google Reader, you can paste URL's into the "add new feed" box or, and this is the cool part, if you're using Firefox (haven't tried Opera), you can drag another tab into the box. Google will then take the address and work out what the RSS feed actually is, even if the tab you're dragging doesn't have the feed itself open. Which is clever and extremely convenient.
In IE7, tabs get focused the second you click on them, not when you release, and so the tab-dragging is not possible. You're left with having to highlight the URL, copy, change tabs, paste...
This is the sort of fuss that made Palm so many loyal customers when mobile versions of Windows was the competition. "The zen of Palm" they called it. I can hardly refer to the Zen of Firefox, but maybe the Purgatory of Microsoft would be accurate.