I have with that idea- and it's certainly enticing- is the used book angle. I'm not up-to-date with eBook pricing but they generally seem to be of a higher price than most used books. The majority of the books I've purchased over the years have been of the used variety and making the switch to more expensive electronic versions (albeit less expensive than buying new physical) is a serious increase in expenditures.

And that doesn't even cover off the used books that I have found that are now out of print and/or will never be converted to electronic format.