Twitter-to-FriendFeed
How it works:
1. They retrieve your Twitter friends
2. They retrieve your FF subscriptions, and cross-check the usernames against your Twitter friends. The ones that match are left out of the next step.
3. The usernames of the un-matched Twitter friends are used to query profiles on FF
4. All hits are returned, with FF profiles who point back to the original Twitter account being considered “verified”