MS really have struggled to improve their shell in any significant and useful way over the past generations.

Granted the new start menu is a good effort but still feels clumsy to use.  The new search box in the start menu means I never search through folders looking for shortcuts.  But if you have Vista installed on a slower PC or your using a prior version of Windows then install Launchy, it's faster and nicer.

The sidebar may tickle the fancy of some, but I quickly lost interest in it and ended up turning it off.  Most novice PC users don't even know what to do with it.

Other than that, I think the Windows Vista shell is functionally boring.

Flip 3D is prettier than MacOS's Expose, but it's not useful and as a result I only use Flip 3D to show off Vistas live previews and fancy rendering capabilities to my peers.

The thumbnail-ing with Alt+tab is rather useless as it's currently implemented.  The thumbnails are too small to easily identify each running application.  TaskSwitcherXP is far superior.  TaskSwitchXP takes advantage of the fact that for the most part, it's still easier to identify an application by it's icon.  Having multiple of the same icon is when a preview is most useful, and the preview provided by TaskSwitchXP is large enough to tell the difference between two running copies of PuTTY.

Vista's ability to display windows thumbnails as a tooltip on the task bar is also not that great when you can get this same functionality with VisualTaskTips for XP.  VisualTaskTips produce thumbnails that are again larger and therefore more useful.  And whilst Vista displays live previews of you application, who cares - live previews doesn't make it more useful.

So what else could have Microsoft done with Vista?  Well the idea that applications should be displayed on the taskbar in the order they were opened just doesn't make sense.  This is something that should have been changed back when Windows 98 was released.  Why can't we move them around into a more logical order?  Microsoft couldn't think of this, but fortunately someone else did and created Taskbar Shuffle.

The changes to the way Explorer displays folder paths is very nice but will probably confuse novice users.  Surely they could have included split views by now so we can more easily copy files between two locations - File Manager from Windows 3 days allowed this and it still hasn't returned.

Multiple-monitor support is pathetic in Vista.  We still can't set different wallpapers for different monitors, or have it span multiple monitors.  We can't make a single window maximise across more than one monitor.  We can't make the Start bar expand across more than one monitor.  We can't do anything we couldn't already do in Windows 95.

It seems to me there is more they could yet still do - ideas that have yet to be implemented by other developers.  One I would like to see is the ability to dim inactive windows.  There is very little visual difference between an active and inactive window which makes it easy to start typing in the wrong one.  This is also true for XP.  The ability to dim an inactive windows would ensure it is extremely clear which is the active window.  There are some programs out there that attempt to do this, but none work well.

I think Vistas shell is uninspired and unnecessarily restrictive.  We shouldn't have to rely on other software to get some basic and useful functions for the Windows shell anymore.