I feel a little silly for wanting to suggest this, but I'll throw in my coins regardless.

How about a simple greeting system like Poke from Facebook? Except poking is an annoyance. Maybe "Send a Hello"? I mean, it just sounds really nice to wake up to a notification saying someone dropped by my profile to say hi without their needing to drop a VM.

(And it helps people rekindle faded relationships too, in case one dropped off for some time for unknown reasons, etc.)

[b]tl;dr[/b] Simple "I dropped by to check on you" gesture. Subtle greeting system?