I have a massive dead-tree collection, but having e-versions is much more convenient.
I mean, seriously, I love reading from a physical book, but being able to tote one around is not always feasible (or comfortable, depending on the size/format).
I used to read on my Palm T|X using eReader, then upgraded my dumb phone to a Galaxy S II 'Epic 4G Touch' which is my primary ereader using a combination of Cool Reader (it has a nice night mode as well as easily adjustable brightness by swiping the left border of the screen, as well as reading the .pdb files I generated for using on my PDA) and Kindle for Android (when absolutely necessary).
The problem with reading on my phone is that I blow my battery reading and have to recharge it in the middle of the day or risk killing the phone.
I also have a Galaxy Tab 2 7.0 with the same two readers on it, which is a nicer, easier to read screen, but heavier than the phone, and of course not quite as portable.
I have wanted a dedicated reader for some time, but had decided to wait for a decent color e-ink display to hit the market. I ended up getting the Tab 2 instead, for various reasons.