I am lucky to have a brilliant sister. We have a long history of reading together. Whenever I read a good book as a kid, I always passed it down to her, even though she's five years younger. Needless to say, she was always reading well beyond her age group even in elementary school. By the time she got to college, she was making recommendations to me, and now we've reached a kind of reading equilibrium.
Perhaps because we have both always read so much, we've also made good editors for each other. I helped her with college applications, English papers, etc. and she has read almost everything I've ever written. We've had issues at times. She can get very critical, although strangely, she's never been terribly critical of me. She gets very critical of my characters. I kid you not, these are some of the comments she's given me:
"I want to punch her right now."
"What a spoiled brat! Why is he even listening to her?"
"Someone should throw a snowball in her face!"
All of these also came from Mina. I learned a lot from this criticism, even though at the time it just made me laugh. (Funny Side Note: My mom saw a copy of those comments and had a talk with my sister about being nicer to me. We're both in our twenties and do not need her to intervene, but it was adorable.) My sister and I did have an issue at the beginning of Safira. Based on early talks we had about the book, she saw my MC progressing quickly, but I intended for her to develop slowly and steadily throughout the book. I think my sister found this a little frustrating at first, but once she was assured that Safira would indeed grow up by the end of the book - and become awesome, by the way - she relaxed.
The point of this post is to appreciate a good beta reader. I have the very best beta reader in my sister, and I have a few other gems, too. I know from reading my sister's papers (and reading all of the comments she sends me on my work) just how much time goes into editing and being a beta reader. It's not something I take lightly. If somebody has read your book from start to finish and given you honest and constructive feedback, that is a time to be grateful. The problem with me is that if I ever get this book published, I'm going to want to thank every single person who reads it, even though they won't be giving me feedback.
That sounds like a wonderful problem to have.
UPDATE (5/2/13): While at the time I wrote this, I thought it was a good idea to have seven beta readers, I now realize it's not. Seven is too many to keep track of, and not all readers are equally helpful. It's best to choose readers carefully and focus on quality over quantity.