Hmm, interesting question (++). For me I consider giving people credit part of the Thank You. So I think updating the node with links to the solutions I found helpful and links to the users who posted them is the best way to go. This has the added benefit of letting future viewers also know what worked and who helped. A /msg can also personalize it and makes sure that the user knows that they helped you out (since they may not see the update). Of course, it goes without saying that you should upvote the helpful nodes.