Sounds good in theory, but login-links are a security issue, because they:
show up in browser history
can be pasted accidentally somewhere
are send usually unencrypted via email
Don't get me wrong, I play with the idea of login-links as well, but they have some drawbacks that one should at least be aware of.
This is where I really love the Token Authenticatable module in Devise (for Rails).
Your rails app can start by just collecting emails. As your app grows, you can then turn that table into a Devise User model. Turn on token auth. and your emails can now include links that auto-login users.