I sent about 20 books to bookscan.us as well. So far the response time is quite a bit faster than 1dollarscan (I think the latter has just gotten some well-deserved popularity after they lowered the Platinum price in December). Bookscan.us doesn't offer the many options that 1ds has, such as Fine Tuning; I like the latter since the raw color scans are kind of huge (100MB+) so I keep them on the PCs and the ereaders get the fine-tuned files that are much smaller (10MB).
The books I sent Bookscan.us are to be scanned in B&W (per my specification) so hopefully the file size would be reasonable. Once this batch is done and I am happy, I will be sending more just because I am happy with the responsiveness and the status communications. BTW, Bookscan.us will also return the cut-up book back to you for a fee if you want, which is a nice option.
I will continue using both services as long as they perform as expected. I have a whole lot of books to go through and was contemplating buying another 1dollarscan Platinum membership but will try using both vendors for different types of books instead.