Nice project. Keep in mind I'm just a tire-kicker on HN, but it would be neat to have dynamic periodic reminders similar to spaced repetition learning algorithms except you rate the strength of the relationship after each session. Strong ratings mean you can see them a little less frequently; weak means you should see them (a little) more frequently.

Ideally this would let you maximize the number of maintainable acquaintances. Unfortunately (for some), it would also prevent any from getting too close. :)