I have few complaints about its functionality, but it's rather ugly, requires a stylus for some operations, and generally doesn't fit in. Also, as mentioned above, it lacks a discoverable fullscreen exit method, which means it would confuse the heck out of many new users. Mostly things like that. Maemo being reasonably close to mainstream distributions, a large amount of Linux apps will run with just a recompile, but their usability and level of integration will vary widely, and may not be suitable for mobile use without modifications. That's the issue with Evince right now.

EDIT: Hmm... I just looked down and realized I had Evince open, and furthermore that I was thinking of an older version of it when I wrote this. It's actually not as bad as I made it sound, but it still could use some work.

UPDATE:
@imperiallight: Yes, it has Rotate Left/Right options, and the operations are tolerably fast.