Is there a "best practice" for Organization in Xcode 4?

I'm coming from the java world, where files/classes should be layed out well structured within packages/folders in my understanding.

What is the best practice in Xcode4? I couldn't find an Apple guideline for this yet. If anyone can push me to the right document, I'd be happy.

In case there is no document: what is the best to do so? I find it a bit odd to have all of the Classes in one project folder - either inside the Xcode-view or the file structure (strangely filestructure doesn't seem to equal the visual structure in Xcode). Of course the project will be on version-control (on GitHub).

Many thanks in advance!