One of the difficulties that I've had with XCode is that the SDE is not as slick as I'm used to. When combined with some of the peculiarities of the language, it is more painful to code in this than in Eclipse for Java or Visual Studio for C# (especially with the Resharper plugin). I've found that JetBrains, the creators of IntellJ and Resharper have created a SDE called AppCode for Objective C. I've tried it and it is far easier to use for most things than XCode (either 3 or 4). Right now the Beta is free, and you can sign up for a 50% discount on the final product.
I highly recommend it. The smart code completion is far better, it can automatically make properties for you, it has far better refactoring, and navigation.
The only downsides are that it doesn't support interface builder, or modifying a SQL-Lite database. Also if you want to modify your project settings you still need to boot up XCode.