MacTalk Australia have written a great review of hidden.
"Hidden can track your Mac’s location, plus provide you with photos from the iSight’s camera and more. How much do you ask? A one off fee of $20 per laptop. Not much to have a ‘just-in-case’ policy for your laptop."
You can check it out here: http://www.mactalk.com.au/2010/03/19/mac-app- review-hidden/