Or sometimes, everything actually goes well, and they get an answer! So they thank the poster… only to be told that on Stack Overflow, “please” and “thank you” are considered noise. All these experiences add up to making Stack Overflow a very unwelcoming place for far too many.
This was given as a complaint on this blog. Maybe something was already done about this; I'm not such an insider. But let me offer a suggestion for this particular problem (and maybe a few others with it).
The moderators should have an option of making comments "personal comments" that are only visible to the questioner and the answerer or commentor. This way people who appreciate it can see the thank-you, and nobody gets offended, and the site is saved from noise.