Sunrise,
Good topic. I think many of us struggle with boundaries.
I do believe that each situation is an individual one. For example, there are boundaries about touching that I wouldn't expect someone to cross and if they did, then I would react strongly. However, there are other boundaries that I have had difficulty with also.
Recently, a person who I had a working relationship with crossed my personal boundaries, and our business relationship boundaries, with unrealistic expectations. I sort of extricated myself from the situation without saying too much at all (as Mouse said). I did tell her that she needed to communicate with me but I used my silence that followed to communicate my dissatisfaction. She "got" the message. I wanted to just tell her to f off but I held my tongue and smiled. She had her own stuff going on and it was painfully obvious that this was her stuff and not mine.
I also recently discussed something with T about my relationship with one of my sisters. At times, it is wonderful and we share the same sense of humor. At others, she is rageful and crosses many boundaries. T said I have to protect myself her when she is like that. But I realized it doesn't mean I don't see her anymore. I talk to her when I sense she is safe, and keep the visits shorter and less frequent. Also, when she "acts up" I cut the conversation or visit short.
I think you are on the right track by observing.