Today I'm handing the post over to one of my Beta readers, Katie. (She is also my self proclaimed biggest fan - even turned in a resume for the position.)
Normally when I'm reading through a book, I think to myself, "I wonder what the author decided happened in this guy's past to make him act this way? How many planets are in this sci-fi? What happened to this country/universe/family in the ancient history of this story?" And that's where knowing the person who is writing the book comes in handy.
As Amy types up new books I get the pleasure of reading through them, usually as each chapter is finished. She will also send me rough drafts of queries, or a full novel that has been picked through by her other betas. While I may not be the best typist or speller, typos and other grammar issues usually scream out at me from other people's writing (those who can't do, teach - that type of thing). This skill doesn't usually get used while being Amy's beta until it is a proposed final draft and she is trying to tighten it up.
When she sends full chapters she is looking for feedback on the overall story lines and for any plot holes. With everything going on in someone's head while they are writing a novel, they may not catch that they haven't yet spoken of a cat that's in the story line, or they may not notice that they decided to kill off that character two chapters ago and didn't remove him later on while revising.
One of the things I love most of being a beta is firsthand seeing a story be born. I'm a huge fan of Amy's writing (the biggest fan, actually) and love the ideas and worlds that she creates for her characters. The only time it gets hard to be her beta is when she revises a story that I have already engrained in my head as being perfect. That's a small price to pay for getting to enjoy her reading!