[antonlitvinenko]

With single device - you're right... but this becomes really a problem when you expect your customers to use multiple devices: computers at home, at work, smartphone, iPad...

how would you suggest your customer which login to use the first time she tries to sign in on another device?

[Drbble]

Ask for username/email, then key off that. 80% solved.

[rogerbinns]

Would that be my personal email account, my gmail account, my other gmail account, my university/alumni address, my work email or the other work email?