It's just a fun thing to do. If someone occasionally decides to take a camera (oh I don't know, maybe after watching a marathon of Next Top Model and being terribly bored at home) and take some pictures of themselves and post on Facebook, it's not a big deal. It doesn't mean the person is somehow self-absorbed or egoistical.
Now if self-portraits are ALL a person ever takes and posts, then there may be some ego problem (unless the person is a model, but then I'd recommend getting a professional photographer).