I'm quite polite, but I haven't noticed significant upvoting of the thankyou nodes I posted in my last query. One of them was downvoted, although it did say that the previous poster didn't successfully answer my question.

However, I think thankyou nodes are useful to indicate whether the answer was successful. I don't really expect them to be upvoted though, as apart from giving some feedback they often don't contain information strictly useful, so I think they should be neither up or downvoted.