The UI/UX/API/mobile and desktop apps/backends, all of which you dispatch off without thinking, are all non-trivial to get right. The fact that evernote doesn't have too much competition right now should tell you something.
More than text files? Yes, there's some binary file support too. "Ooh"
OCR is not hard. They probably just use http://code.google.com/p/tesseract-ocr/
The fact that they don't have 'competition' proves nothing. Maybe nobody wants their 'product' because it's not useful. As others have commented even here, who've actually tried to "get it" multiple times, it's really not useful for a lot of people - they just don't see the point.
Maybe the lack of people copying their "product" is because it's just marketing fluff around a solution to a problem that doesn't exist (really, very much, for most people, apparently).