Suddenly, my trusty taskbar on Vista, which was set to auto-hide (very handy for saving space on laptops), has stopped to auto-hide. It just sticks, regardless of the other settings under Taskbar Properties/Taskbar/. Even tried checking and unchecking "Auto-hide the taskbar" several times, to no avail.
Having recently played with placing making my second display a primary display inside Control Panel/Appearance and Personalization/Personalization/Display Settings, this might have been the cause. Dunno.
I first found the solution to be TaskbarSlapper (downloadable program, works fine, no spyware as far as I know), but that only worked one time, and now, it doesn't work anymore.
So I dug deeper, and here is an inelegant solution that, however, worked for me: From: http://www.annoyances.org/exec/forum/winvista/1189550818.
To solve your problem: Open Task Manager (Ctrl-Shift-Esc), select the ^Processes page, highlight 'explorer.exe' and click the 'End Process' button.
The Taskbar will vanish.
Now go to the ^Applications page and click the 'New task...' button. Type "explorer" and click OK.
The Taskbar will return and behave correctly. Until the next time.
One downside of this fix: some apps which insert their icons into the Systray at boot time may not do so again. The app will still be still running -- it's just that it will have no Systray icon.
As I say, it worked for me, with the above mentioned side effects. Beats rebooting Vista, at least for me.
If this works for you, or not, leave me a comment.
If you have a better solution, leave me a comment below.