Yeah, if you look at your circles, the friends that aren't on G+ show up with an email icon in their bubble indicating that you are sharing with them via email

Yeah, if you look at your circles, the friends that aren't on G+ show up with an email icon in their bubble indicating that you are sharing with them via email only. I've suggested multiple times that the same icon be shown in the suggestions list. It really sucks that it is not on by default.