The points were connected to an old reputation system. This button appeared on every post
and members could give good or bad rep to the poster. This was abused by some members and caused arguments and a bad atmosphere on the forum, so it was dumped in favour of the thanks button.
As
Mal has already explained, you get five points for every thanks You receive. Once you have collected enough of these points and made a certain number of posts you get promoted to the next user rank. (Junior Member to Vintage Member only)
More info about the user classes can be found here,
http://vintage-erotica-forum.com/t15...ber-ranks.html