Sorry, couldn't resist it. :) 
I've put a link in today's Riters R Us ( http://community.livejournal.com/riters_r_us/ )  post to a really informative meta entry about being and choosing a beta. It mentions some things we haven't given much thought to on here - for instance, the fact that betas with widely differing writing skills and reading preferences probably aren't going to be very compatible.  It's an excellent point, although I'd have to argue that one unskilled writer helping another with the same skill level isn't likely to help her improve... Unfortunately, we see that on here all the time. A beta is thanked, and yet the fic submitted is full of grammatical and punctuation errors.  Or it really needs work on the characterizations, or the plot logic.   A beta who cannot spot those problems isn't going to be very useful in helping the author to turn out a fic that meets our criteria for posting.

However, the idea that you're going to do a better job beta'ing something you actually want to read is undoubtedly true. There's a lot of good stuff to think about in the post. I recommend it.

Rather than start a new thread, I figured I'd drag this one out to remind readers that they can contribute to the fandom by offering their services as a beta reader. If you have good grammar and punctuation skills, like to read stories before everyone else sees them, and are willing to help a writer out, why not add your name to the new beta list? (See the menu at the left of the home page for that link). 

A reminder to authors: we do not "vet" the betas. They are all volunteers trying to help out, and their skill levels will vary. You may want to try to line up more than one so as to take advantage of their differing strengths.The one who spots your developing plot holes and can suggest ways to fix them, may not be the best one to correct your grammar and spelling.  The one who can teach you to write grammatically and smoothly, may not have a clue how to help you structure a story.  I realize that it is difficult for someone who is struggling with mechanical issues to successfully judge the abilities of a beta, but it's possible you may have to try a couple before you come up with a good one. A knowledgeable beta should be giving you the grammar or punctuation rule that you are violating so that you can learn it and avoid making that same mistake in the future.  If yours cannot do that, perhaps you need someone with stronger technical skills.

Reminder to betas: please help your authors improve their skills by sharing the rules with them, rather than just correcting their mistakes without ever teaching them to avoid making them.  And don't forget to offer suggestions and advice about the story itself.