Abraham Williams

Twitter provides a Sign in with Twitter flow that is OAuth but provides a faster redirect if it is an existing user of your service and they are already authenticated with Twitter.

http://apiwiki.twitter.com/Sign-in-with-Twitter

If you are building a Twitter centric application this makes a lot of since to use and you won't have to implement an entire alternate authentication method like OpenID.

Be careful if you let users authenticate with both Twitter and LinkedIn as users will inadvertently create two accounts and need them to be merged.