Windows 7 Extends Run As Options
Windows Vista users had the option to run an application as the system administrator instead of the currently logged in user. There was however no option in the context menu to run the application as a different user. The current build of Windows 7 has this feature which should come in handy for several users who need the functionality. The context menu entry “Run As Different User” is only visible when pressing the SHIFT key before right-clicking the file icon.

[...] Vía | Windows 7 News [...]
Actually you have had this functionality way before this. You can runas any user you choose even in XP. I’m not sure if you knew that already. I’m guessing you are only commenting on the fact they have added a context menu entry right?!? No big deal I’d say.
[...] changes to the upcoming operating system to increase productivity. We already mentioned the new Run As User option in the [right-click Shift] context menu. Another addition falling into the same category is [...]