If you have a choice in framework, I'd actually recommend not learning Ruby through Rails. I'd learn it through Sinatra. Sinatra is a lightweight web framework (Rails is a heavyweight), and it has a lot less "magic", so it's more plain Ruby and less connecting framework components together.

Not knocking Rails, it's just that you'll get a really narrow and somewhat skewed perception of Ruby if you learn it through Rails (you'll have no way of easily separating the Rails magic from plain Ruby as you learn things).