We currently notify unregistered users with an @ message on Twitter when someone...

		loquace on May 25, 2010 \| parent \| context \| favorite \| on: Ask HN: Please review my Twitter dating app ;) We currently notify unregistered users with an @ message on Twitter when someone likes their profile, or sends them a message or a smile. We only ever send one of these messages, and never again, if they don't join after that. (See http://twitter.com/PlentyOfTwps for examples.) When the user is registered, we contact them via email.

Ah, well that's both technically feasible and non-evil then. Good stuff!