I haven't talked about one of my favorite new features of Xcode 4 and LLVM, because I wasn't sure of the NDA status. However, the cat's out of the bag now, so I feel like it's safe to mention. The iPhone Simulator in Xcode 4 now uses the Modern ABI (yet it's still correctly uses 32-bit datatypes!), so we can use synthesized instance variables in our iPhone applications and use the simulator. On top of that, if you choose to use LLVM instead of GCC, one of the (many) benefits you'll get is that @synthesize declaration is now assumed. If you don't need to specify anything on the @synthesize declaration (like a different setter or getter name) and your property isn't @dynamic, you can justleave it off. This feature isn't turned on by default (yet), but see Pilky's blog post for instructions on enabling this feature.
Less code to write? Boo-yeah! Count me in!
I believe (though I haven't confirmed this yet) that you can write code this way and still target older releases back to 3.0. If anyone knows otherwise, please let me know and I'll spread the word, though.