I'd say I get thanked ~10-15% of the time in F (domestically). A few times, the Captain has even come around to say thanks (this seems to happen more often on 757 due to the 2L boarding).
In coach, I think the only time they've noticed is when I booked last minute and am sitting halfway back, but able to board with the PREM cabin. I had one F/A once jokingly say: "I bet you DMs didn't even know there were this many rows on a 757". haha.