I just stumbiled upon a great article about levereging ARC in your objective C applications. I'm doing ARC in a Cocoa Touch (iPad) app right now and it's helped make a couple extra things clear.
For example, I now know that ARC is a target relative switch that can be enabled/disabled. This is helpful for a project with additional compilation targets in it. Recently I added CorePlot to a project and I wish I had known about this ARC switch. Instead I had merged everything to non-ARC for that project, but now that I'm keen to the ARC switch, that won't about happen again.