1. Providers
1.1. Facebook
1.1.1. Pros
1.1.1.1. Common
1.1.1.2. Sharing
1.1.1.3. Comprehensive profile
1.1.1.4. Network/Friends
1.1.1.5. Less chance for fake users
1.1.1.6. Very good API support
1.1.1.6.1. Web
1.1.1.6.2. Mobile
1.1.1.6.3. Open graph
1.1.2. Cons
1.1.2.1. Fear of all eggs in the same basket
1.1.2.2. Privacy?
1.1.2.3. Security expectations
1.2. Twitter
1.2.1. Pros
1.2.1.1. Sharing
1.2.1.2. Communication
1.2.1.3. Common
1.2.2. Cons
1.2.2.1. No email
1.3. Windows Live
1.3.1. Pros
1.3.1.1. Microsoft is refocusing all their products to a single identity
1.3.1.1.1. Future reach may change
1.3.2. Cons
1.3.2.1. Obsolete service/API? New windows 8 coming
1.3.2.2. Unknown
1.3.2.3. Low usage
1.3.2.4. Bad API
1.4. Google
1.4.1. Pros
1.4.1.1. Future potential because of Android
1.4.1.2. Google+ accounts is a Google priority
1.4.2. Cons
1.4.2.1. Cumbersome API
1.5. Janrain
1.5.1. Pros
1.5.1.1. One API
1.5.1.2. Many providers
1.5.2. Cons
1.5.2.1. Costly
1.5.2.2. Single point of failure
1.5.2.3. Basic feature set
2. General
2.1. Pros
2.1.1. No verification of email required
2.1.2. Easier registration
2.1.3. Can be disable since it is optional
2.2. Cons
2.2.1. Not a replacement for security
2.2.2. May lead to confusing ux
2.2.3. Subject to external Influence
2.2.3.1. Privacy
2.2.3.2. Usage
2.2.3.3. Uptime
2.2.3.4. Terms of usage
2.2.3.5. Lockout
3. Options
3.1. Only Facebook
3.1.1. Pros
3.1.1.1. Less options
3.1.1.1.1. Less clutter on interface
3.1.1.1.2. Better UI
3.1.1.1.3. Native implementation
3.1.1.2. Practically an industry standard
3.1.1.2.1. Entire business depends on it
3.1.1.2.2. Platform for the social graph
3.1.1.2.3. Billion users
3.1.1.3. Comprehensive profile
3.1.1.3.1. Mobile
3.1.1.3.2. Email
3.1.1.3.3. Interests
3.1.1.3.4. Friends
3.1.1.3.5. Address
3.1.1.3.6. Location
3.1.1.4. Communication
3.1.1.4.1. Messages
3.1.1.4.2. Notifications
3.1.1.4.3. Sharing
3.1.1.5. Free
3.1.2. Cons
3.2. Janrain (Facebook/Google/Live/++)
3.2.1. Pros
3.2.1.1. One implementation to rule them all
3.2.2. Cons
3.2.2.1. Not 100% native
3.2.2.1.1. Missing some functionality
3.2.2.2. Costs money
3.3. None (only our own account)
3.3.1. Pros
3.3.2. Cons