Eehh. :S Just the thought of having something tight and liquid being sprayed around my wang before it solidifies makes me feel uncomfortable. It's probably not the most erotic thing to do in the heat of the moment either - Heck, even normal condoms are an inconvenience, akin to wrapping cellophane around your tongue. Now imagine spraying something cold around your tongue that'd numb the taste before you enjoy a large ice cream sundae or a tastey pizza or some other food that you'd normally find very tastey and enjoyable - Wouldn't it really, really put you off?
IMO I don't think this is a good contraceptive alternative, and I'm gonna repeat what some people have said here already - What if there's a defect and it misses a spot? And imagine peeling it off afterwards. :P Ick! :S
EDIT:
Alector thought of something.

What if you're the type who doesn't shave thier bits, and you accidently sprayed it onto your pubic hair or so. Now, imagine peeling it off. >.< lol