Are social exchange websites safe?

[Trevor]

You want people who are genuinely interested in what you are offering. Having the subscriber number grow looks great, but if they are pretend people who'll never return and recommend you to their friends, then it is pretty useless.

These sites may or may not hurt you, but definitely will not help you, as I mentioned above. Google watches these sort of sites and those that continue to operate in a harmless fashion exist, but anything they offer has no value in rankings. Many of them will eventually be suspended. Google wants to connect people with what they want, which is about a site being optimized for the keywords that someone is searching for. It is not simply about having a large following.