One, the kensington barrel locks can be picked using a toilet paper tube, here is a link with a video:
http://www.boingboing.net/2005/05/18...laptop_lo.html
Any of the motion sensor locks that have an alarm are not very loud (hold your hand over the speaker and i doubt anyone will hear) and can be easily defeated my submerging it in a glass of water.
I just picked up a PC Guardian Notebook Guardian Ultra lock, see here:
http://www.pcguardiananti-theft.com/...ltra_2001.html
The cable is twice as thick, one review noted it took over ten minutes to saw through using a hacksaw, compared to 30 seconds or less for the standard kensington. Also, not susceptible to picking, and is harder to pry. Prying is probably on of the biggest weakness of laptop locks. Stick a screwdriver in between to laptop and lock, and pull. But, this lock takes measures to prevent this. I can post what i think about it when it arrives, bought it off amazon.