Hey Skrommel, just played around with Ghoster a bit.
While it migth be classified as a "toy", I find it very appealing - it could be pretty useful when one needs to code for a while, keeping you from being distracted too much by things in the background.
However, there's a little bug - after I exited Ghoster, at least two of my windows still had "always on top" enabled - one was mIRC which was easy to fix, the other was firefox which I'll probably have to close down and re-start after posting this message.
Also, when selecting tabs (probably also MDI windows), the active window flashes as if it was being ghosted and then re-enabled. I think the on-top stickyness might be related to this, since both mIRC and FireFox are tabbed, and I switched tabs in both apps while running Ghoster.