People (me for instance) who aren't yet using Facebook will be no more/less likely to sign-up after viewing The Social Network. In other words, The Social Network will have zero negative effect on Facebook; but at the same time, I don't think it's going to have must positive effect either.
However, people who have resisted Facebook thus far (like me), will likely NEVER use it after seeing something like Catfish. And I think, to some extent, avid users of Facebook could potentially start thinking twice about certain uses of the Facebook site.
Basically, in a nutshell, Catfish is a truly disturbing look at where the Internet has gone (and where it's headed) while The Social Network exists as an intense character study of an individual who is basically Daniel Plainview in a hoodie.