Mix are awful in my experience. Ordered photobooks from many different providers and the quality of the paper and printing is shocking. Customer service was dreadful when I asked for it to be reprinted.
Did you find someone else you like? Also, what was the main problem? All the reviews I've seen, here and other blogs, have loved Mixbook. I was all set to use them for the first of many books, but now I'm not so sure.
Forever.com/Forever_Print is another great site! FOREVER recently launched an online photo book application, which fills out its other products of permanent digital storage, media conversion and digital scrapbooking. The books I have gotten printed are beautiful and the application is easy to use!