I regularly work away and the Kindle means I can find any quiet nook in a pub in which to read without needing to care about the ambient lighting. Even better, I have an illuminated screen that isn't shining a blue-bright light in my eyes that will disturb my sleep.
We need better performing (faster and higher resolution) screens along with more care taken to format texts for reading on an e-reader - the latter is being addressed by Standard eBooks which is a Gutenberg project to address typographical quirks and generally provide a better eBook reading experience.
We aren't there yet, but we are getting there.