As purely a model flyer with no intention of violating any rules related to the registered hobby/model flyer that I will be after the 21st, should I have a reason to expect some kind of interaction with an FAA official? Because if people like me start getting visits for no obvious reason other than the fact that we registered, there is going to be some hell to pay to calm us down. It is reminiscent of Nazi Germany when the government shows up at your door because you took part in a govt. registration program. It's people like me who will vote these goons out of office. It's people more extreme than me (and they are out there) who will be influenced by their govt. to incite violence in response to tactics like that should they start.
Realistically there's no reason for the model/hobby flyer to have any interaction with the FAA. The only way the FAA would come a'knockin' was if they received a complaint from someone. That someone would most likely be a local LEA since the FAA sent a memo out to all LEA's earlier this year describing how they would like them to interact with the FAA should they encounter people they feel were violating the law or flying recklessly. OTH, it would not be a bad idea to maintain a list of where and when you were doing any flying just in case someone else did a dirty deed that caused them to look in your general direction. As small as the tail numbers will be on our stuff whoever does the reporting will have to have some might fine vision.
The larger issue will be in educating the LEA's and their representatives. I've already been approached by officers from a state agency asking about basically what was right and what was wrong, and how to deal with the wrong if and when they encountered it. So those that fly responsibly and understand how to do that, if you happen to know people that are cops or similar take a moment to strike up a friendly conversation about what you do and be prepared to state the differences between the good guys and the bad guys. In all likelihood your conversation will be the first they've had about multirotor operations and some of them are really interested in getting into it themselves. There's not much to it really, 400' max altitude, maintain line of sight, don't put others or their property at risk, right of way to manned aviation, steer clear of towered airports unless first having a conversation with them, and don't fly for hire without a 333 waiver.
An interesting side benefit is you'll find you became their "go to" guy for further info, you'll make a friend that might end up very beneficial, and may end up teaching a few of them how to fly their own stuff.
