The issue with Facebook (Google+ and the other social sites) is that Scouts under 13 can't legally use them (see here for Facebook: https://www.facebook.com/help/?faq=210644045634222). This is to deal with COPPA, which restricts what websites can do with information for youth under 13. Out of our troop of 110 boys, we have a fairly large number of boys who wouldn't be able to use the public sites. This makes it a non-starter for us.
As I understand it, you can allow registration on a private website for your unit and not run afoul of the COPPA requirements.
As someone who maintains district and unit websites, this is painful but it is the law and we are Scouters, so we follow the law.
As for the earlier comments about custom web sites, I would agree unless you are using a content management system to keep information up to date. If you have someone hand-coding a site or using tools like Dreamweaver to make a site, it won't stay up to date and in the end isn't worth it. I've converted several to a content management system and integrated calendars from Google, embed videos from Youtube, tweets from Twitter and photos from SmugMug. We get the benefit from leveraging the other sites but have it all consolidated in one place.