Support legacy iPhone users

Question

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

Answer 1

progmr has already given a very good answer; one thing worth adding is some hard data:

http://www.appleinsider.com/articles/10/07/22/chitika_ios_4_already_powering_50_of_iphone_traffic.html

ie. 50% of the iphone users (that are installing and using apps with ads in them as of a July 2010) are still running versions prior to 4.0.