I haven't done the 'sign up for everything' piece, but my wife and I have made a conscious effort to minimize what we post about our daughter online. We don't refer to her by name, we don't tag her in photos, we minimize photos of her. Now, we both have active online lives, so we talk about her online, but hopefully in a respectful manner. Sometimes it is really hard to resist sharing that cute photo, simply because sites, FB in particular, make sharing so easy, but I think we've found a path that works for us.
I think a lot of parents, especially less privacy aware and/or tech savvy ones, are not aware of what they are doing for their kids when they post photos online. (Just as few non technical folks I have talked to know that the links at the top of Google search results are ads.) They just want to share information (mostly pictures) with friends and families.