The best feature of Apple's iOS4 update that is overshadowed by background applications, folders, etc? Apple now enables calendar event creation contextually and within email exchanges. When a date and time are written in an email - iOS4 will hyperlink the text (ie Tomorrow at 8:30am) and allow you to add it to your calendar. It's a huge time saver and something I have long wanted in Outlook (where calendaring is a *massive* pain) and in GMail (where there is similar, but flaky functionality).
Apple consistently pulls off these relatively small features and integrates them seamlessly. Why Microsoft hasn't figured out a similar feature within Outlook... over its many years... signals the shift in the two companies' success in consumer products / development.