I have been a bit skeptical so far about investing in yet another piece of technology to meet an individual need by buying a Kindle, Nook or other brand of electronic book reader.
I have been using the free Amazon Kindle app on my smartphone (htc desire) for over a year to read books on my commute and at leisure. I like that I use one device - with facilities for mobile phone, email, internet, music, camera and now e-book use. Another bonus is that I only have to carry one power charger with usb socket and a short micro usb cable in my handbag. I charge my smartphone overnight but run the battery fully down once a month to prolong battery life - are people doing this with Kindles?
The screen size of smartphone is smaller, at 2" x 4", than, for example, a Kindle* with 3.5" x 5" with keyboard. Other Kindles probably now have larger screens than this example but I have not found the page size too small and I can still increase the font size as required. I can also bookmark pages and make notes.
I currently have a selection of 42 books, including the Hitchhiker's series

, on my smartphone, could keep more on the phone's external memory card or use cloud storage but I have also downloaded more to my PC using the PC version of the same app. There can be some good e-book deals to be had in many genres, for example the eight book Works of Friedrich Nietzsche at £0.49p, so you can overlap with or supplement your physical book collection.
It is likely I will also buy a Kindle at some point in the future, or be 'gifted' an older model* so a.n.other can justify getting a new model...