IE 9 works only with Windows 7 and Vista. That's it. XP users? You're out of luck. There's no IE 9 for XP. Mind you, by NetMarketShare's count, the majority of Windows users are still running XP, 55%, to 23% running Windows 7 and 11% with Vista, but there's still no IE 9 for you.
Of course, Microsoft also doesn't support IE 9 on Mac OS X or Linux either. The reason, of course, is that Microsoft wants to sell you Windows 7, even if you don't need or want it.
Windows fans tell me that no one would ever run the 64-bit version of IE. Funny, the IE 9 download process still insists that that 64-bit Windows users install the inferior 64-bit version and, those folks, rather naturally, assume that they should run the 64-bit browser. You shouldn't. No one should. Instead, just run IE normally and don't search down IE-64 instead. When you install the 64-bit version you also get the 32-bit one.
When I asked Microsoft why they even bothered to ship IE-64 bits, never mind insisting that it be downloaded, they never got back to me.
On the other hand, IE 9 is much more secure than any previous version of IE, but that doesn't mean it's as secure as its rivals. For example, these days attacking Web-plugins, such as Adobe Flash, is every hacker's favorite new trick. IE 9 doesn't alert you if you're not running the latest plug-in, which Firefox does with its Plug-In Checker or automatically update them ala Chrome with its built-in PDF and Flash software.
IE 9's Tracking Protection feature lets you set your browser so advertisers can't track you as you wander the Web. There's still a hole in it though so if you have two sets of rules with a conflict over whether you should or shouldn't be tracked, it will default to letting you be tracked. So, sure, IE 9 is safer than earlier versions of IE, but if it's security you're after, Chrome and Firefox appear to be the better choices.
So, if you want a great Web browser for your Windows machine, or any other system, I recommend Chrome 10. Firefox 4 is also worth considering. But, IE 9? The best I can say is that if you absolutely insist on running a Microsoft browser, and you're not running XP and you're sure you're running the 32-bit version then yes, it's an acceptable choice.
I try to like Opera, but it's never worked that well for me. The biggest new feature in Opera 11 is extension support, something everyone else has been supporting for years.
There are some features I like. For example, I rather like being able to stack tabs rather than having a never-ending line of tabs across the top of my display.
The basic interface combines the now popular stripped down look, with the red Menu button on the top left window border. I also like that the new address bar, ala Firefox 4, shows a site's security information. To use this feature, you drag and drop tabs on each other. To get to them you then hover with your mouse cursor over the stack's base tab.
Opera also includes its own mail client -- once a common feature but increasingly rare -- and it's been improved considerably. In addition, it includes its own BitTorrent client. If you like the idea of a do-it-all, all-in-one Internet program, Opera deserves your attention.
Is it worth trying? Sure? It can be quite fast, and maybe the features will appeal to you. To me, it's an interesting, but in the end, not particularly engaging Web browser. Your usage may vary.