Facebook censoring Google+ invites
According to this video, when you post an update on Facebook that invites your friends to join Google+, Facebook secretly censors that post. They don't tell you, and they don't tell your friend.
This is why you can't trust
Facebook everything you see on YouTube. ; )
UPDATE: Some commenters are reporting that sending invites on Facebook does work for them, or is censored only in the Top News view. Possibilities that explain this include: 1) the video is a fake; 2) Facebook censored, then stopped censoring; or 3) Facebook is censoring only some people, using Edgerank somehow to censor or not censor according to some unpublished rules.