Office 2007 and the Ribbon introduced the concept of "Key Tips".

In short, every single command in the Ribbon receives a letter which you can press to activate that command. ... The letters are indicated by small "KeyTips" which indicate the letter to press to activate the control. KeyTips are displayed using the Alt key, so using them feels similar to how menu navigation works in Windows.

(Source: http://blogs.msdn.com/jensenh/archive/2006/04/12/574930.aspx)

An example of the Key Tips can be shown as follows. In this diagram, the use has pressed the ALT key, and is awaiting further input.

Are there any WPF Open Source examples of "Key Tips"?

How would you go about implementing something like this feature in a generic way (i.e. not requiring a Ribbon)? How would you implement this using a MVVM pattern (given that ICommand does not support InputBindings).

Note: ActiPro have implemented this feature in their implementation of a Ribbon, but they have not released source code.