If users generally dislike facebook, but continue to use it, it's a bad situation to be in for Facebook. It indicates that people are using the product because of its network effects and despite the product itself.
It means that if anything begins to actually challenge the network effect of facebook, they will be in a very tough spot.
A telling moment that happened two nights ago for me. A friend from ~8 years ago came to visit and we wanted to send a joking message out to a few people from the old group of friends we used to hang out with.
The conversation was literally:
A: "Post it to Facebook and tag everyone." B: "Ehhh. It would be funnier to find an old email thread and reply to it."
We went with B. It seemed like a better idea, plus we weren't sure if folks in the group checked Facebook. But everyone reads email -- and sure enough, we got life updates from the whole gang within 12 hours.
It could mean a lot of things. Maybe it means it's cool to say you dislike FB. Maybe it means people feel badly about their addiction to social networks in general. My point is that it could mean a million things that may very well have nothing to do with FB.
Furthermore, what you're describing sounds to me like the best situation for any company to be in. Ever. You make something that is so compelling and you solve a certain problem so well that people tolerate it despite its deficiencies.
That's the opposite of what I'm describing. I'm describing making something that people don't find compelling, that doesn't solve their problems, but they use it because it's their only option (the network effect).
FaceBook already has had companies brand themselves as the anti-FaceBook.