... there is a critical mass on FB that G+ is going to have a hard time beating. Many of the people I interact with on FB are family members (who won't switch because they have no need to: it's a wonder they're on FB at all) and old friends from High School and College, many of whom won't switch because they see no point in doing so (and, as I said, probably have family links that they don't want to loose.)
Unfortunately even though (if?) G+ is better, it's unlikely that people will will switch en masse. It is highly unlikely that G+ will do to FB what FB did to MySpace.