I dig my iPhone, but when I switched over from my Blackberry, I was very surprised at how many steps it takes to find out about new email.
On the Blackberry, there is an external light that flashes a different color based on new messages. Then, when you log in to the BB home screen, the Messages icon has a little badge indicating new messages, also by color. So either one or zero interactions is enough.
On the iPhone, you get neither of these things. You have to log in at a minimum. Then, the mail icon will tell you the number of unread messages, but gives no indication of whether they are new since you last checked.
So you then need to go into the Mail app, then into your Inbox, to see what’s new.
Not only is this relatively time-consuming (when repeated throughout the day), but that much interaction is work for the battery.
Battery life on mobile devices is all about micromanagement. Software developers look at every operation and ask, “can we not do this right now?”. It’s always looking for ways not to refresh the screen, to minimize use of radios (like WiFi or GPS), to avoid calculations that don’t benefit the end user right now. It adds up!
So if the iPhone would just give some indication of new messages without logging in (as it does with SMS, for example), this would save both end-user time and several dozen battery-draining operations a day. I bet this would save several minutes of battery life (and brain time) for an email junkie like me.