For years on a WinXP system I used to have a great little 'app' that added an 'Ext' column into the 'sort buttons' in the right pane of Windows Explorer (default 'sort buttons' are of the type 'Name', 'Size', 'Type' etc.). Unfortunately that 'app' doesn't work in Win7.
What that 'app' did was allow sorting of files by the filename
extension (e.g. doc, mp3, wav, odt etc.).
If this could be managed for Classic Explorer it would be a great addition. Initially, it might sound like nothing much to be desired, but a few weeks of having that functionality in Explorer would convince most people otherwise.
In case I'm not explaining my idea very well please have a quick look at this website where there is a graphic illustration of what the 'app' does and detail of the advantage it provides. (If you had time and a spare WinXP system to test it on you can download the 'installer' from the same webpage and give it a try.)
http://www.xrayz.co.uk/extension-column/