I must say I have a lot of epubs which I'm reading on my Kindle. Calibre does a great job to convert mobi <---> epub without any (seeable) conversion lost.
Well, there is the DRM obstacle but this is another discussion point.
Btw. all the B&N Nook guys out there. Your epub format isn't ADE compatible as well and uses a proprietary DRM scheme. So you're not that different to the Amazon guys.