Now that iPhone SDK 4.0 is available for download, and iOS 4.0 will be available for consumers shortly, does it make sense to start using the new features available in the 4
I personally usually target one major release behind (i.e., target 3.1 instead of 4.0), that usually gives me a window of "Have you updated your phone in the last year?" But depending on your application, you may be able to make use of multitasking or other features that are only in 4.0. Then, it's a matter of what you think your users will want right away. If you think they can wait a bit, see how things go; if you find a lot of users are moving to 4.0 quickly, then push out your changes.