The new Win+0..9 shortcut seems good, but it only seems useful for the first few apps in the taskbar. Is it possible to make Windows prefix the icon with a number 1 to 9 ?
7+ Taskbar Numberer adds numbers to your taskbar items, so you can see right away what keyboard shortcut is assigned to each item. Optionally, the numbers can appear only when the Windows key is down.
No, it is not possible.
I think it has already been asked on SuperUser. And it's also listed on Windows 7 Taskforce (here for instance).