What did it for me is that they have a bunch of Wrox "Professional" and "Programmer-to-Programmer" books available (and more coming). I carry about twenty pounds of Wrox books around in my car, so I have them available at work and at home. (When "the check" from the VCs comes in, we'll buy copies for the office, but I'm not holding my breath). The idea of being able to carry my technical library around in my briefcase (or in my pocket, even) is compelling. Add in the ability to text-search and to bookmark, and it's a no-brainer. The ability to grab a technical book in a minute, anytime anywhere, is priceless for someone like me - jack of all trades and master of whatever the client is paying me for this week