In case you don't know what a beta is (though I imagine that around here everyone knows), it's a person who in effect acts as an editor for you... a person who gets to read your work before you release it to the general public, to give you hints on how to make your fic better (grammatically, story-wise, or whatever).
Was poking around on aff.net today, where I saw a whole category for people either looking for the services of a beta reader or offering themselves as betas for hire. I usually don't use one myself, but I often end up acting as one (anything going up on my page automatically gets the grammar/ awkward wording check, just to make sure it's generally readable).
Anyone around here use one? Do you find it helps you? What does your beta look for---just grammar, or just story holes? And if you don't, why not?
I'm not sure why I've never got into the habit of using them. It certainly seems like a good idea to have another pair of eyes looking at something before you send it out...