The training wheels have come off of the latest version of Internet Explorer, as Microsoft unleashes version 9 of the world's most heavily used browser this evening at an event at the South by Southwest Interactive Festival (SXSW) in Austin, Texas. Internet Explorer 9 (download after 9 p.m. PT) debuts to the public not only as the fastest, most standards-compliant version of IE yet, but also as one that can stand up and compete on features and looks with Mozilla Firefox, Google Chrome, Apple Safari, and the Opera browser. Along with IE's new features, though, Microsoft has a clear message for Windows XP users: hurry up and upgrade to Windows 7 already.

Microsoft's official explanation for why Internet Explorer 9 doesn't support Windows XP, the operating system that runs on an estimated 40 percent to 50 percent of the world's computers, is that the graphics card-powered hardware acceleration that helps the browser load pages faster doesn't work properly with the device drivers on Windows XP. However, at least one other browser, Firefox 4 release candidate 1, offers full hardware acceleration across multiple operating systems, including Windows XP.

The lack of support for Windows XP aside, Internet Explorer 9 is a fantastic browser when compared with its predecessors, and competitive against its toughening rivals. The browser offers some great new features, such as Pinned sites, a revamped search box, and add-on performance impact notifications.

Pinned sites create a tighter integration between the browser and desktop by creating site-specific browsers. Drag a tab onto the Windows 7 desktop taskbar, and depending on the site developer's coding you can get site-specific jump lists, unread e-mail notifications, or streaming media player controls. Other major sites that have Pinned integration include Groupon, CNN, Pandora, Hulu, Slacker, Facebook, Twitter, and eBay.

The interface isn't the only part of IE9 that's gone back to basics. Notifications, such as the session recovery warning shown here, appear at the bottom of the browser window and won't "grab your focus" and prevent you from continuing to browse. (Credit: Screenshot by Seth Rosenblatt/CNET)

Meanwhile, the new unified search box manages to include all the functionality of the old search box, such as changing search providers on the fly, while introducing on-the-fly searching so that as you type you see a relevant list of Web results, bookmarks, and browsing history.

The add-on performance notification is a small but useful feature that warns you when an add-on is slowing down the browser. You can customize what level of impact is warned for, too.

The performance of the browser itself has been lauded since last year when Microsoft rolled out developer's previews. Over the course of the following year, the developer's previews, betas, and release candidate version of IE 9 were downloaded more than 25 million times, and amounted to around 2 percent of all installed versions of Internet Explorer on Windows 7 by the time the release candidate was published.

For an in-depth review of Internet Explorer 9, check back here at 9 p.m. PT when Microsoft makes the browser available to the public.