I don't have a PnS. If I am invited to a wedding and the BnG hint at "...and maybe you can get some good ones while you're there..." or something like that, I generally want to leave my gear at home (unless I'm really close to them - then they wouldn't hint, they would just ask or it would be assumed). If they don't hint at anything and they are important to me, I don't care about the pro photographer (as I'm not competing with him). Do you know what all those PnS'ers are doing? They are taking pictures for themselves, because they care about the BnG and want something to remember it by. Just because I own some professional bodies and "L" glass doesn't mean I shouldn't be able to do the same thing.
Now, where it becomes disrespectful is when you start competing with the hired photog. Basically, if you're walking around and people think you might be the hired photog, you are probably crossing the line. I don't have a list of required shots in my mind or have my camera up to my face the whole time. It's generally in my wife's purse - with ONE lens - and I take it out a maximum of maybe ten minutes through out the entire day. Now, if some are wanting to shoot for the duration of the wedding then I agree with everyone saying "leave the gear." There's already a photographer working. But if you're bringing your camera because A) you don't have a PnS yourself, B) you want these photos for your own sake (just like everyone else with their cell phones and PnS's) and C) you've only brought it to take a handful of pictures, then I see no problem in bringing your camera and a lens.