Why should patrons have to come to the desk? The modern library should be a place where librarians don't wait for people to come with questions, rather they roam the library looking for confused patrons aimlessly studying the shelves trying to make sense of that bizarre thing called Dewey.
Freescale claims it's going to have a stripped down tablet running either Google Chrome or Linux by summer that will sell for only $200--powerful enough to run an online book catalog remotely. Lenovo and HP both have models in work in the 500 to 1000 range for people who need something more powerful and running Windows. If you really want to be cool you could go with the rumored Apple Tablet, but likely that will be nothing more than an overpriced, oversized, iPod touch.