I strongly feel that thank you notes or e-mail are absolutely not brown-nosing, or a bribe, or excessive, or anything like that. Sure, a gift, or flowers, or a bribe of any sort is EXTREMELY inappropriate.
But if someone did something that you are appreciative for...you tell him or her! It's just plain etiquette and an act of courtesy.
I've spoken to make interviewers about this, and one in particular who has been interviewing for around 15 years said that when you receive a note from someone, especially since not many people send thank you notes, it really helps him remember the person and highlights that they are interested in the school!
You should not be writing notes just to make yourself look good anyway, so why should it matter if it makes a difference? You should stand behind your actions and your academic history proudly, and let them decide. I just do it to let the school know how much I enjoyed my day there and how I know how hard everyone on the adcom committee works throughout eat interview cycle.
Sure, for some interviewees, it won't make an iota of difference. But firstly, I don't feel that it's the point, and second, it really can't HURT. NO one would get offended at one, unless there's a check inside.
I don't mean to sound bitter, it's just frustrating that so few people write letters anymore and that some feel so worried about what will add and take away points from the adcom's opinion.