Lately when using Windows 7 on my laptop, I like to keep the taskbar at the top. It just seems more natural to me to keep these controls at eye level than at the bottom.
One of the problems you encounter with this setup is the occasional window opening underneath the task bar, completely obscuring the titlebar such that you can't move it or click its buttons. The workaround is to either move the taskbar or Alt-Space + M and move down with the arrow keys or mouse. I'm aware you can also use Win+Up/Left/Right to maximize or position left/right.
But, if anybody remembers Windows 95, this has always been a problem with the taskbar at the top. Has Windows 7 managed to fix this with some option I'm not aware of?