Subject recruitment and Facebook

Does it seem ethically problematic to recruit experimental subjects by way of a facebook post?  I’m thinking of a project that has permission to recruit by word-of-mouth, by announcements posted to listservs, by posters hung up around campus or elsewhere in the city or passed out in person, etc.  That is, permission for a pretty broad range of recruitment activities is in place.  This is for a low-to-no-risk speech perception experiment.  One could begin the facebook post with “People in X city:” or such, since it’s an in-person experiment.  Facebook seems like a combination of a listserv with word-of-mouth.  Just to clarify:  I haven’t done this, but I’ve considered it.  I’m curious what others think.