I get a little ticked when someone lifts one of my arrangments and doesn't at least give me credit for the version, but I have on real problem with someone singing one of "my" songs.
If, on the other hand, they sing a song that I wrote, and they know that I wrote it, I can get downright hostile. Especially if they didn't bother to get my permission.
Stuff that I have recorded is another matter. What I am talking about are the unrecorded songs that I do in concert or at festivals.
I always try to give credit whenever I can, either to the writer or to the person I learned the song from and I try to avoid doing songs that are a known part of someones repetoire unless I have a very different version.

troll