High pass sharpening is actually the same technique as Unsharp Mask sharpening...it's just a different way to go about it, and with a little more flexibility.
Sharpening is one of those things that few people fully understand (myself included). There are a few books on the subject, one that I've been meaning to read is called 'The Art of Sharpening' (or something like that).
You could also Google yourself several days worth of reading on it.
In a nutshell, I don't think there are any hard rules when it comes to sharpening (or photography in general, really). Sharpening is usually done to taste, so everyone is different. And different photos will respond better to different methods or strengths of sharpening.