After our recent discussion, we've now added the ability to thank users for contributing to the forum. You should now see a little thumb at the top of each post; clicking on it adds a thank you for that post, and these are displayed below the text and also tallied up for each user. If you click on the thumb by accident, you can cancel the thanks by clicking on the thumb again (which will now have an X over it).
Although the karma option got the most votes, the karma modifications available didn't have very good feedback or support (or karma, if you will...). The thanks add-in seems to be much more reliable. Touch wood. I also like the fact that it's post-specific, so contributors get good feedback on exactly what has been well-received.
As usual, reply to this thread if you encounter any problems.