There has been a lot of writing about how you should never give your email password to anyone. Usually it's the social networks that say they want to help you find your friends etc. I quite like OAuths restaurant analogy:
Giving your email account password to a social network site so they can look up your friends is the same thing as going to dinner and giving your ATM card and PIN code to the waiter when it’s time to pay.
I recently got an invitation for the location based social network Brightkite, and they had a quite elegant solution to this problem.
Since this is all publicly available information, I kind of think it's alright for them to do. (The question whether Twitter should expose this data about me is a different story.)
What Brightkite gets here is a map between their users and their Twitter accounts. And using the twitter API they can match my friends at twitter with other Brighkite users that has optionally supplied their twitter names.
This way I don't have to enter any password at all. Sure it only works for the networks that exposes my user friends lists publicly, but quite often this is the case anyways.
I think this idea could be pushed even further. Given that most users use the same usernames for all their social networks, Brightkite could actually just go to the Twitter API's and get see if there was a user named username and if it exists, ask me whether it was me. Here are some API's that could used:
On the other hand, it is a bit creepy knowing that all this information about me is out there for anyone to read. I also think that anyone who uses these API's to get data about users need to make it in a transparent way so not to give the feeling that they are snooping around.