I'm a university student who loves writing in my spare time-- I currently have only one story up, though I've been writing for several years. I've beta'd before and I've found it to be an interesting and very fun process. I currently beta for one person, though I'm looking to take more people on as partners. It takes me at most three days to edit a chapter 7,000 words long, so I'm fairly quick.
I'm pretty open about how people want to have their stuff beta'd. You may want to do it in chunks, send it to me in a word document by e-mail, or use an online writing service: I don't really mind what you choose. I've beta'd through Zoho the most, though I've also done it one-on-one with a hard-copy. Whatever you choose, I'm fine with it.
My beta style is not complex. I go through it fixing spelling and grammar, along with making note of glaring characterization or technical issues. I'll write in brackets my problem and then, after doing a couple more read-throughs to see if I've caught everything, I'll send it back to you. Then we'll discuss the errors and my general opinion of the chapter. What we do this over-- IM, phone, livejournal, e-mail-- is up to you. Once you've looked over the errors and decided what to do with them, you send it back and I'll look it over again, one last time. After that, if I find nothing that I've overlooked, you'll have my blessing to post it up.
About my corrections: I do not feel that I am the end-all. It is 100% possible I am not right-- writing is very subjective, so if something I say doesn't ring true for you, ignore it. I'm here in an advisory role only. I am not the writer of your story. Tell me if you disagree (politely, though!) and I'll leave it alone. :)
On to expectations, then! I'll confess to being not very picky. I'm looking more for someone with good ideas than a master of spelling and grammar. I'm willing to help someone work out things like tenses and voice. While I'm happy to work with advanced writers, I'm more interested in helping people who are at a basic or intermediate level figure out the details of writing. All I ask is that you be at least functionally literate, with a large helping of ideas.
There's only one more thing I ask from potential writers: I am a full-time university student. Please be understanding if I need more than three days to edit. I have papers to do and tests to study for. I promise that I will never take more than a week to edit something, but sometimes your story will need to go on the back-burner temporarily.