One of our former wedding coordinators, and now bride-to-be, mentioned that she is having a problem with keeping her wedding details secret. There are many reasons you might want to keep your plans private - from not hurting someone's feelings who isn't going to be invited to not getting negative comments on the design, decor, dress, etc. So how do you have some privacy in this social-media-overload age? Don't do it. The easiest way to avoid this problem is not to talk about the wedding at all. Not always practical though!
Use Facebook Lists to filter who sees your wedding-related posts. Click on "Lists" on the left hand side, then click "Create New List." Set up a list called "Wedding Guests" or "Bridesmaids," then add certain people to that list. Then, when you go to post a status or photo, select that list from the dropdown box and only those people will see that update.
Keeping track of ideas - don't use Pinterest. I have a blast checking things out on Pinterest. But, if you want to keep your wedding ideas private, don't use it for this purpose. Check out a free program like Evernote, that has a Web Clipper feature. It's the same basic concept, but private. Or, consider using a shared folder like Dropbox if you need to collaborate with your mom, maid of honor, fiance, etc.
Think about what you share online - and if you wouldn't talk about it publicly, don't talk about it online! Happy planning...