It did come up recently in some user feedback, and reignited the issue, but it's hard for people to agree on the best solution. From time to time there's a request for rep points, but they have been dismissed because they are to easy to game (certainly my experience from other forums). Others would like some kind of upvote system, such as on Stack Overflow, but to me at least, that makes threads too confusing. I prefer to follow the discussion as it happened and decide for myself. Then there are suggestions for some kind of Like/thumbs up button, but again, that seems too easy to game to me. There are also some forum add-ons (or at least one) that can be used as a kind of thankyou system. Then there's the suggestion of a private button that you could hit once for a member in a calendar year, which would count as a vote towards the end of year awards. But the downside is that the thanks is not public then. All the same, I still don't see the problem with just saying thanks within a thread if someone has helped you.