My former HBS colleague Andy McAfee has a great column at Forbes.com about how companies such as Apple, Amazon, and Google have been able to enhance their technologies and make them more complex without frustrating consumers. McAfee focuses on four key principles:
1. Evolve, don't upgrade: Focus on making a series of smaller incremental improvements rather than major upgrades that can be disconcerting and confusing to users.
2. Keep the core interface constant: Think about the consistency of the Amazon's website or Apple's iPod interface.
3. Don't even talk about it: Let the consumers discover the enhancements on their own.
4. Let the users opt in: Provide new features that are optional for the consumer, and that the customer can begin to use as they become comfortable with these technological changes. Think about the App Store from Apple.
By the way, if you are not familiar with Andy's work, I highly suggest that you check out his blog.