At any given point in time, I'll usually have about 10+ windows open on my computer.  So when I need to access something on my desktop, which is quite often; I'll hit the show desktop icon to quickly minimize all the windows.  Problem is, my show desktop icon was missing.  Its not a normal program shortcut, so you can't just copy and paste shortcuts as you normally would with a program.  After a bit of googling, I was able to find a quick way to get it back.  Here's how:

 1.  Click Start,  then Run...  The Run Dialog should appear.
 2.  In the textbox, paste the following command: regsvr32 /n /i:U shell32.dll
 3.  Your show desktop icon should be as good as new.

I just spent a good portion of the day tryoubleshooting why we were getting this javascript error in out prod environment, but not in our development environment.  Specifically, the error was happening with a Telerik Popup control, but judging from a few google searches, I think that it is more specific to the ASP.Net Ajax extensions.

There a probably quite a few different causes of this problem, but I was able to fix it by removing the <xhtmlConformance mode="Legacy"/> node in my web.config file.  The xhtmlConformance setting appears to determine how controls render to the clients browser. The default is transitional.  It does not seem to play well with the Asp.net Ajax extensions if you have it set to legacy.

 UPDATE:
Looks like Scott Guthrie has already posted a gotcha on this.  Amazing that a google search for the error wouldn't pull it up.