One of my systems is a dedicated HTPC with 55" DLP TV connected via HDMI-HDMI, and an LCD connected via DVI-DVI on a nVidia GT 240 video card.
Whenever the TV or monitor is turned on or off, any open application windows jump from display to display. So if I'm encoding a DVD and the LCD goes to sleep, when I come back the app window has gone to the TV (whether the TV is on or off). If I happen to have the app window minimized, I can't use a hot key to move it back. I have to turn on the TV and drag it back.
Add to that my desktop icons mover around, even though my LCD is set as the primary. This same set up worked wonderfully with XP. Everything stayed where I put it regardless of displays going on and off.
If anyone one knows how to turn of the monitor detection "feature" I'd really appreciate it.