If you use an instant message tool, people who want to contact you can know when you are online (that’s half the point of the software after all). But the Big Brother-ish IM Watching.net goes one step further and keeps an eye on the whereabouts of IM users 24/7 (as long as they have elected to make their online status publicly known). So now you can (for example) confront a teleworker or spouse with ‘evidence’ they weren’t at their computers for several hours they said they were. Oooh! Very sinister… Of course it was only a matter of time.
I don’t use IM much myself, and only make my online status known to people on my buddy list so it wouldn’t affect me.