On the downside so far I notice that it does not always have the "instant app change" that iOS has, if I leave the Zinio app (which Samsung use for magazines in their "Reader's Hub"), it has to start up again when I come back to it, this is unfortunate. Also I have so far a bit of trouble with it losing Net connection, on both my wifi networks, let's see how that plays out, it really should not be common.
(Note, in the Zinio app you can zoom in to your heart's content, I think it works pretty well even on a 5.3-inch screen. I won't hesitate to read on it when I don't have my iPad around.)
On another note, the Kindle Fire started shipping today, so we should get early reviews soon. I'm starting to lean a little towards thinking that it may be the 7-inch tablet/reader which is the "tweener" though, and five inches right for pockets, and ten inches or larger right for stands and bookholders.