I know the NYPL will let me check out ebooks, but the result is wrapped in layers of DRM that tie it to my computer (or, with some work, a Sony Reader or B&N Nook). One thing I'm sure of: e-reading will succeed if and only if the text is truly portable across many devices. My most frequent reading location will be a tablet-sized e-reader, but I may want to access the material on a desktop, laptop, work computer, public location, phone, etc. Without that functionality, we've taken a step backwards from physical books (which, for the price of inconvenience, I can have wherever I want).
I don't have a problem with DRM itself. In fact, I'd embrace it if only I could access the data anywhere. What's so difficult about that? Every e-reader app for the iPad provides syncing capabilities with its respective hardware; surely the NYPL can figure something out!
But I may be asking too much for the NYPL's books to be freely available, so how about this: I will gladly rent books rather than buy them. When I purchase a book from Amazon, B&N, etc., instead of just downloading the text straightaway, ask me how long I want the book for (1 day, 1 week, 1 month, forever) and charge me accordingly. Maybe the book costs $10 to own, but I can have it for a week for only $3. And after a week, I'm locked out. Need more time? Three more dollars, please!
Or how about this - instead of a la carte pricing or rentals, I'll pay a flat rate for unlimited reading. Maybe it's a few hundred dollars (I have no idea what the efficient level would be off the top of my head) to subscribe to Amazon's library. Lock the ebooks to my devices so I can't distribute them and you got yourself a deal.
This can't be difficult to implement on the technology side, though I imagine it would meet some resistance on the publishing side. The evidence for success is strong, however - look at movies and music, which have both embraced successful rental or subscription plans.
One of the keys to this model could be how hard it is to access the filesystems of the devices in questions (iOS devices most notoriously). Putting a DRM'd file on a computer is, let's face it, an invitation for someone to hack and redistribute the information freely. But because we can be confident that consumers will use controlled/closed devices to access their ebooks, part of the hacking threat is mitigated.
But again, there's nothing revolutionary about this idea. Movies and music have been doing it for some time. We just need to expand our conception of "multimedia" to include text as well.