I found this on nibbanam.com:
The epub format is for portable devices such as ipad, kindle and other
electronic ink readers, and some smartphones.
Although I think kindle does not support epub, but there's free
software available that can convert from epub to a format a kindle can
I may get an e-ink reader such as a kindle someday. It's getting almost
cheap enough (139$) to be in impulse buy. The advantage of e-ink is you
can read for 3-4 hours before your eyes get tired due to eyestrain,
compared to 1-2 hours in a normal LCD display for example. Also, the
e-ink is readable outdoors under real sun light, unlike laptops.