Well, if you wanted to created spyware, be careful, who you give it to, you could get in a lot of trouble.
In my mind, an ultimate "watcher" would include a STMP client to send they're keystrokes and mouse events. This is probably what you're thinking of also.
A sample KeyBoardHook:
Processing Global Mouse and Keyboard Hooks in C#
A sample SMTP client:
Sending Mails in .NET Framework