I wouldn't, for the most part. Not saying that it would or wouldn't work out, but I don't feel comfortable with doing that. Going through friends who might know someone there could help, as that way you wouldn't be a complete stranger. The only instances where I might do so is if I know someone there with which we share the same background (e.g. same college) which provides some sort of common ground.

I've only ever cold e-mailed recruiters (or some job listing e-mail), which is pretty much expected.