The Reputation system has been replaced with 'Likes' (in the last upgrade).
These are more or less the same thing.
If you see a reply on the forums that you like you can click the little blue 'Like this' button in the lower right hand corner of the post and it will be counted towards that member's reputation. Their reputation level shows up in their profile page. Likes to a post will also let you see who has liked a post.
It's like a system specifically for members to show appreciation to others for their contributions to the forums.
It's not the same and not linked in any way to the site's Karma system which is managed by the TamaGuides and Admin. In other words, having a lot of likes or reputation does not automatically mean you should get positive karma points from the Guides
(I only mention that because we get members from time to time who think the Guides should give them a good karma point because someone has given their posts a lot of likes)