We liked Techcrunch's write up of a presentation about the Android Design Principles (ADP) at Google I/O. The presentation summarised the ADP and gave some insight into how they were developed. They cited recent social science research suggesting that positive composite experiences need to outnumber negative experiences in order for the whole experience to be reported as positive.
We need to offer gentle affordances and kind messaging to let your user know what is happening, rather than accusatory and intrusive ‘error’ messages of old. We also need to work hard at impressing our users with wondrous details so that if anything does go wrong, they are more forgiving.
Always aim to leave your user happy.