I honestly find this discussion very interesting.
Much as I don't like overzealous friends/family who do an extreme uncle bob at weddings who do get in the way of the professional photographer, I think there's a point to make about the wedding photographer who is not so professional. Essentially, some wedding photographers are also guys with cameras looking to make a quick buck - they don't like shooting weddings as much as the next person due to the hassle and stress involved, but do it for the money.
My issue with them starts when they aren't able to deliver quality shots, regardless of whether uncle bobs get in the way. And like you said, wedding photography is about trust and people skills. Some can get downright rude, although it is pretty rare (anyone with a brain can tell that it is bad for business to be rude to the couple or their guests, so I guess most just try to ignore the guests that get in their way and take it in their stride). The good ones will probably communicate with such people, or even make friends with the overzealous uncle bobs to make them understand that the wedding photog needs space to work.
Unfortunately, my impression of the state of the industry is that bad professionals outnumber the good ones at a high ratio. While I'm sure that the problems raised doesn't lie with experience veterans like those posting in this thread, the problems do exist, especially when the couples cheap out and hire budget photogs, or even those part of a wedding package. Yeah, I know, pay peanuts, get monkeys applies here. Not exactly the fault of the real professional photog; the barriers of entry to the industry isn't exactly high if you don't go for high end cameras, editing software - which is the case for most budget photogs.
I would think that the degree of professionalism of such photographers is the question that I, as a guest with a photography hobby is concerned with. Most wedding photogs are ok with guests shooting with small pns, handphones. Most are even okay with those shooting with fancy rangefinders, or more advanced systems like m43rds. However when a guest/relative appears with huge dslr attached with flash unit and the works, I find inevitable that the wedding photog goes 'Oh no, another darn uncle bob playing with his camera....." in his mind, whether the guest gets in his way or not.
The important part is how the professional wedding photographer handles the situation, and of course, it is not his/her fault if the shots do get ruined by the uncle bob. But the instant condemnation of the guest-with-advanced-camera is what I have issue with, especially when it exhibits itself in the behavior of photog towards a guest. Wedding photography is at its core, a service industry. Award winning photos are a bonus. But many people who does this line 'professionally' forgets the core tenet, which is service.
The point I'm trying to make here is that wedding photographers, professional or not, should not categorize all non-professionals as just another uncle bob. Sure, there are extreme guests that I might make it a point to pull them out of the way of the professional should I know them. But there are also the crappy professionals who don't handle such situations well when they should, and worst of all, aren't able to deliver the final results.