This may be old news, but I was surprised to discover when reading an ebook yesterday that there was no simple way to copy a snippet (and, say, paste it into a twitter app). Selecting the text in either the Kindle or iBooks app on an iPhone or iPad doesn't give you the usual option to copy it (see image below).
I assume this is due to a concern over copyright violation, but that seems a bit extreme as it makes it difficult to copy even small snippets for note-taking or other writing tasks (and I'm all in favor of reasonable copyright protection). It's absurd that it's easier for me to tweet a sentence from a paper book to an iDevice than it is to tweet from an ebook on that same device.
The second thing I noticed was that highlighting a passage -- a feature all the e-readers advertise -- has a huge usability issue. You can't highlight a passage that goes over a page boundary. In the situation pictured above I tried all the gestures I could think of to move the marker onto the next page while still highlighting, but nothing worked. I then tried decreasing the text size to make everything fit on one page. That still left a page break, but after a number of increase/decrease text operations the pagination magically shifted so that I got the passage I wanted onto one pagein order to highlight.