Not all of the new features in IE 9 are tied to Windows 7. The browser also includes the following new and improved features:
Download Manager with SmartScreen Filter. At long last, IE gains a download manager. And while it works pretty much as expected, Microsoft has of course added integration with its SmartScreen Filter technologies. And in IE 9, these technologies have been boosted with the introduction of a new download reputation rating that is based not just on the publisher and file name, but also on real world usage. So if the reputation of a file you wish to download is good, IE 9 won't stand in your way. But if the reputation is bad, you'll receive a warning. IE 9 is, to my knowledge, the only browser that attempts to intelligently prevent bad downloads in this fashion. (Other browsers throw up a generic warning for all files, regardless of the source.) And if the success of the Smart Screen Filter thus far is any indication--over 1.2 billion blocked malware and phishing attempts so far--this will likely be a very useful feature indeed.
IE finally gets a download manager.
Add-on Performance Advisor. When you start up IE 9, a built-in performance advisor measures the start up time of the application. And if it falls below a certain threshold, it will provide a warning via the new notification bar, giving you a chance to selectively turn off poor-performing browser add-ons. What's neat about this tool is that the window that appears graphically shows how long each add-on takes to load, and they're sorted with the worst offenders at the top.
The IE 9 add-on performance advisor.
The problem with the performance advisor, of course, is that virtually anyone who's used IE for any amount of time is going to have a number of add-ons loading, and these add-ons will trigger the warning a bit too frequently. And since there's no obvious off switch, it can get annoying.
You'll be seeing this one a lot.
Hang recovery. Anyone who's used Windows for any amount of time is familiar with the application hang dialog, where Windows informs you that Application X has stopped responding and gives you the option to kill it, restart it, or wait. Now that functionality is coming to IE 9, and not just to the browser as a whole but to individual tabs. When a web site freezes or responds too slowly, tab process isolation prevents it from affecting other tabs, and IE lets you know what happened and then recovers the containing tab, reloading the site.
Now web sites can fail just like real apps.