Obviously, it's very popular to share photos and videos on Facebook, and it's understandable that those forms of media will take up a large percentage of small mobile screens. Not really an issue specific to advertisements.
The IPO was overvalued in my opinion, but I don't think the stock price is a great indicator of the future of the company. That said, I think a decline is possible, but will it happen soon? I don't know. Maybe the backlash will come from kids whose parents are essentially building profiles for them.