Here is a nice visual style for Windows 7, which makes the taskbar invisible; well not exactly invisible … but well almost!
What the style does is that, it removes the line that defined the edge of the taskbar so that it blends in with the desktop.
Sure you may still see the blur, where the taskbar used to be. But try choosing a plain background and adjust the colouring in Personalize to get the floating icon on an invisible taskbar look.
Do create a system restore point first!