Your problem isn't that covering your WebCam isn't a good idea (it is). It's that there's little market for a solution -- electrical, scotch, gaffer, duct, or other tape works just fine. A small scrap of paper or Post-It will keep adhesive from marring the lens. That's a $0.01 solution I doubt you could ever hope to compete with (though I hear suckers are born on an aggressive schedule).

That said, from a design perspective, I'd very much prefer that devices (laptops, desktops, tablets, phones, monitors, etc.) offered:

1. Hardware indicators of activation of media inputs: camera, microphones, etc.

2. Physical covers or switches to activate/deactivate these. My Thinkpad has a physical switch to activate the WiFi transmitter, but there's no shutter for the camera (I've seen slider doors on some devices), nor can the mic circuits be toggled by a physical control (though I can set my mixer settings via software).

Edit: But see comments elsewhere: stickers which explicitly convey a message about security/privacy and cover lenses could be an interesting angle. Much lower cost, fad/awareness appeal. Possibly even a tie-in with privacy groups (e.g., EFF, etc.). Good schwag.