I'm watching the WWDC2011 and have resisted upgrades so far, but it looks very temping. I usually wait once something new comes out. I'm using Xcode 4.01 and API's from probably march '11. The ARC and other upgrades look great, but are they stable? I haven't heard much so far, so I'm guessing they are. Also I understand the API is backward compatible with iOS 4, is that true?