Originally Posted by vectrum
I asked to make sure that the member has got my thank-you note.
If you click on the "Helpful" link this will not only mark that post as helpful but also add to the members reputation. The member can see this in his User Control Panel and on the "Reputation" tab on his profile.
If you add a follow up with a "Thank you" note to a thread the members that have responded in that thread will see that there is a follow up post in their User Control Panel and in their "Subscribed Threads" page, as long as they don't have intentionally unsubscribed that particular thread. I would think that the regular users here do that rather seldom (I just made a quick check and I am currently subscribed to 5667 threads, with this one 5668).
So the chances that a member misses a "Thank you" are rather small.