I have to admit that I sometimes read on my Xoom in bed when it is dark. Using a dark background and white text, and the light turned down, it is very nice and relaxing.
But in the daytime or on travel I very much prefer reading on the Opus. And if I had to choose only one reading device, I would choose the Opus without any hesitation.
I sometimes make trips where I sleep outdoors in the woods in a hammock under a tarp. The Opus is a great companion, even for extended trips, especially when the days are short. Then I use a Zebralight headlamp, on low, to be able to read in the dark before falling asleep. But I don't dare bring the Opus when it is below freezing, so outdoor reading in the winter has to be on paper.
The accelerometer on mine is turned off as well, A typical example of usless extras.