Yesterday I noticed a node on "Worst Nodes" with a "-1" vote, with contents something like "Thank you for the help. It works now." I immediately upvoted it, and I plan to upvote such nodes in the future.
I see no reason that a person should be penalized for being gracious and thanking those who helped them. I suppose one could say "Bah! No new information content, so it's a waste of time and space." I don't agree, because providing positive feedback (beyond a ++) encourages people to answer questions.
I see that this has been discussed before at Increasing the Signal/Noise ratio of PM, and that most of the responses were positive towards thank-yous (especially if they added new information, but even if they didn't).