link away, you don't need to ask for permission. I will say though if you post about the person's blog let them know only because it will make them feel good. I have customers do these great posts about my jewelry and they don't tell me, I like to thank them.
Well, I would think it's not inappropriate, I guess it would depend on the context, but I generally agree that it's not a problem... I have a series of blogs that I particularly like, and I have listed them on mine, but I also asked the blog owner if it was ok to do so. I got the green light from all of them :)