Looking at Windows 8 broadly, I think the most curious and interesting thing about this new operating system is its dual--and dueling--personalities. This is most obviously seen in Windows 8's new Windows runtime, or WinRT, which provides a Metro-style environment and the Start screen in addition to the more traditional Windows desktop. But it can also be seen in Internet Explorer 10.
IE 10 is a curious beast. There are two versions of this application, really two completely separate applications, in Windows 8. One is a Metro-style app and more locked down and constrained while providing a unique full-screen browsing experience that will be useful on tablets and other highly mobile devices. The other is a traditional desktop application that looks and works much like its predecessor and is fully extensible with third-party add-ons.
The two share the same rendering engines, of course, the same bookmarks, and some basic features like tabs. But the interaction between these two separate IE versions may be unclear to most users. Add a third party browser or two, or muck around with configuring a different browser as the default, and things get even weirder.
So let's discuss a few of what I consider to be IE 10's biggest secrets. Some of these are subtle, but those who upgrade to Windows 8 in particular, this will be worth understanding.
IE 10 Metro is the default
If you perform a clean install of the Windows 8 Consumer Preview, you'll have two versions of IE 10 on your system: IE 10 desktop and IE 10 Metro. The Metro version of IE 10 is the default in such a configuration, so anytime a web browser is needed by the OS, another Metro-style app, or a desktop application, IE 10 Metro is invoked.
Note, too, that in this default configuration, you will find an IE 10 Metro tile on the Windows 8 Start screen, but not an IE 10 desktop tile. There is no way to add an IE 10 tile to the desktop when IE 10 Metro is the default.
Change the default browser to IE 10 desktop
If you'd prefer IE 10 to be the default, and not IE 10 Metro, you can do so by running IE 10 (desktop) and choosing Settings (gear icon), Internet options, and then Programs. In the top of this dialog, change "Choose how you open links" to "Always in Internet Explorer in the desktop".
If you want the IE tile on the Start screen (and any pinned web sites) to open desktop IE instead, also check the box titled "Open Internet Explorer tiles on the desktop."
Trigger IE 10 desktop from IE 10 Metro
Microsoft designed IE 10 Metro to be plug-in free, so you can't install browser add-ons that will work in this version of the browser. We can debate the rationale behind this--Microsoft says a plug-in free IE improves battery life, security, reliability, and privacy for consumers, while critics charge that this browser is horribly limited as a result--but there will be times when you would like to use the capabilities presented by IE add-ons. At these times, you can access the desktop IE 10 instead.
To do so manually, invoke the IE 10 Metro App bar (WINKEY + Z, or by right-clicking anywhere in the browser window) and then click the Page tools button, which resembles a wrench. In the pop-up menu that appears, click View on the desktop. The page you're currently viewing will appear in desktop IE.
Note: I'm surprised there's no "Open tab in desktop IE" or way to tap and hold on a hyperlinked item and open that in desktop IE.
Java, Flash, oh my
As noted earlier, IE 10 Metro will not recognize installed add-ons. This includes useful browser plug-ins like LastPass, but also in-browser aids such as Java and Flash. But these technologies can still be installed in Windows 8, and will work in IE 10 desktop. So if you run into such a page in IE 10 Metro, simply use the View on the desktop tip above to load the page in IE 10 desktop.
Using a third party web browser
Windows 8 of course allows you to install your choice of third party browsers. But when you do so, things can change with IE 10, depending on how other browsers are configured.
If you set a third party browser to the be the default browser in Windows 8, something odd happens to IE 10: The Metro version of the browser disappears. Note that this will only happen if you really set another browser as the default; this requires using the Default Programs UI and not the in-browser controls in an application like Google Chrome.
You can see the change on the Start screen: The tile for IE has changed to a tile for desktop IE, not Metro IE.
The only way to return IE Metro is to make IE the default browser in Default Programs again.
No Metro IE on an upgrade from Windows 7
If you upgrade a Windows 7-based PC to Windows 8, you may notice that the IE tile on the Start screen is for the desktop version of IE 10 and not for the Metro version as expected. This is for the same reason as stated above: You configured a different browser as the default browser before upgrading. So Windows 8 hides IE 10 Metro. Again, to return IE Metro, make IE the default browser using Default Programs.