very nice! I'll give it a shot! I thought about something similar in the past few years. I like the fact that you insist on "no social pressure" and a "gentle" nudge. The goal is not to make the user feel bad :). I also like that you make me import just a small subset of my contacts, to not feel overwhelmed right from the beginning (start small! make it work then make it better).

some quick feedback: - I feel a more natural path to add an "extra checkin" would be from the "flower" in the garden (home page). - I would love to be able to add a date in the checkin. Let's say I know the person I just checked in with told me she has an important event coming up (exam, interview, work deadline, baby...) I'd love to be able to add a specific date for a future checking on a specific topic.