I’ve seen a program similar to that specific to ADDers. It meshes with Windows & uses humour to help nudge you off the computer. In fact, you can even customize the messages in the pop up windows — eg. “Time to shut down now… time for bed… come on… only 60 more seconds… GO TO BED!!”. I think it was in the gadgets section of additudemag.com, or at the virtual adhd conference site adhdconference.com. What a hoot — now, if only you could add a voice to it!