Apparently someone did forget to clean up their mess. Yesterday I installed Chrome Frame to test it. Then my IE8 on Windows 7 64bit started to crash, so this morning I figured I'd better to uninstall it to see what happens. And IE crashed no more.
This afternoon I noticed that I could not open anything hyperlink in Outlook or Word. A dialog pops up saying "this operation has been cancelled due to restrictions in effect on this computer".(Yes, this is Microsoft error msg style, <insert-your-own-joke-here/>) After checking KB310049 with no luck, I started a little Binging and found the answer in the first result. (btw, another search engine returns it at the 2nd result, nice try!).
And Google Chrome Frame is the one to blame. After un-installation, it leaves related registry values under HKEY_CURRENT_USER\Software\Classes as ChromeHTML, instead of htmlfile, which fires up the default browser correctly.
This computer has IE8, Firefox 3.5, Chrome, Safari, Opera installed, so it might be a little bit complicated for Frame's setup routines to handle. However, I've been wanting to do this for a while now: Google engineers, GOTCHA! But, if any googler wants to investigate, just drop me a line and I'm happy to provide MPS report or other troubleshooting data for diagnostics.