In your Gemfile Bundler requires you to tell it where to lookup for gems. For 99.99% of people that is going to be rubygems.org, but it doesn't have to be. There has been talk about making this the default and then allowing someone to turn it off.
edit: The RubyRouges podcast has a great episode with the maintainer of Bundler where a lot of the difficulties with Bundler are discussed in depth. That's the "talk" I was referring too.
well, this is what's insane about Rails these days. we have a value which is correct in 99.99% of the cases, and we are (at best) debating whether or not to make it the default.
I say at best because obviously in my case I did not see a whole lot of debate. the GitHub issue for it is likewise extremely not-discussion-y. wherever the discussion for this incredibly controversial idea is taking place, I haven't seen it.
edit: The RubyRouges podcast has a great episode with the maintainer of Bundler where a lot of the difficulties with Bundler are discussed in depth. That's the "talk" I was referring too.