I use it to give a gong to people who are being really stupid by posting comments that are offensive or abusive. I use it to give kudos to people who contribute something that strikes me as rather special.
But I'm rather sparing with the handing out of either of those.
Q. Do I use this system?
A. There are some advantages to using this system.
Is the person trustworthy
Do they often give useful information
Are they respected in this community
I do my best to fall under all of those categories, as majority of my posts are informational. The more reputation someone has, the better chance of being heard as valid will increase. Reputation is simply an overall quality seen or judged by people in general. Having esteem is one thing, and detesting or loathing is another.