I'm still a proponent of using Mineral oil as a coolant as it is completely non-conductive (eliminating the need to worry about leaks), and also (I'm pretty sure) has a higher specific heat than water, so it can absorb more energy degree for degree. Also, it won't freeze, so, like I said, you can cool it to below freezing temperatures and it still works nice.
Liquid N2, IMO, is still a ridiculous idea for a home user. For a university research team, that's another story.
The point is you have nothing to do with the N2 once it has done its cooling. It has to absorb heat, so it would evaporate, and then you've got N2 gas pouring out of your system (wouldn't that be cooling looking though!). Of course N2 isn't toxic (air is 80% n2 by volume), but if you aren't in a well ventilated area, that may become 95% or higher N2, and you slip peacefully off into dreamland as you slowly die of oxygen depletion. Now is that a worse case scenario or what?