The delayed sign up idea seems to be very potent. Rather than having someone dump all of their information into your database right away (which you then have to save, probably for as long as your app is running), you slowly draw the information out of the user, making the registration process as transparent as possible. If (using your example) Aunt Suzy goes through all the work to sign up, then gets confused, not only does she have a bad taste in her mouth when it comes to your app ("Oh, MyBigApp? Yeah, I tried it once, but after I spent 20 minutes signing up I got confused and left"), she also won't be coming back to use that sign up if she got confused. For the most part, there's no reason to have a user registered for something if they're not going to use it.
In regards to connecting apps, I'm really not convinced being able to do that is a good idea (I hate it when people have to post everything they do online to Facebook, or whatever else they use). There are people who like it, so it may be worth having, but it certainly isn't a feature I would encourage using.