As far as I know, the descriptions based on reputation are all automatically assigned. The negative ones have changed over the years since I've been here, but I haven't noticed a change in the positive rep descriptions. The admins have control over those, as well as the post-count-based titles, which have also changed over the years.
Reputation is given out by other forum members. Every "thanks" is worth three points, for example. The symbol at the bottom of a post that looks like a six-pointed star, next to the "Thanks" button, is used to give out or take away reputation points. The more points and posts someone has, the more reputation points that person gives out/takes away. There is a limit to how many times you can dole out reputation in any 24-hour period, though.
As you've alluded to, the descriptors aren't a great indication of someone's helpfulness. Should I be listened to? Hmmm, maybe sometimes.
But, I tend to keep my mouth shut (well, fingers off of the keyboard) on topics that I don't know about. Years ago, it took a long time to increase or decrease rep, so it tended to better reflect someone's standing in the forum. Nowadays, one person can swing someone else between red and green with one click of that star button, so it can just as easily indicate if you've pleased or upset someone with a lot of points (or if someone is just messing with you
).
