It is old knowledge that if progress bars go faster at the end, the user is happy. In other words, if the progress bar is modified so that it doesn't show the perfect progress percentage, you get a better customer satisfaction.
The same principle applies to other indicators, like battery indicators and mobile phone signal strength. Many phones don't seem to lose battery energy until the very last moment, where it drops fast. Apple has now communicated, that their antenna problem actually isn't that bad, but their signal strength indicator is very sensitive at the coverage levels where this problem was demonstrated. Apple will now "adopt AT&T’s recently recommended formula", which should improve on the problem. That doesn't change the fact, that a piece of rubber can improve the iPhone 4 significantly, of course.
The Google Nexus One has a different approach on battery indicator than most: It starts to drop pretty fast after charging to full level, but when the battery indicator is low and red, you actually still have a lot of energy left - 20% in the indicator means about 20% to go.
What is the best solution? There is a commercial side and a usability side of the problem. The commercial side depends on your business model, and I won't get into that here, but the usability side actually doesn't give a clear answer, either. We have several processes that we want to support:
* If the user needs to plan usage of a limited resource for a specific amount of time (e.g. battery energy for one day), the indicator needs to progress during the entire time span.
* If the user normally doesn't care about usage of a limited resource (battery energy), but may end in a situation where the limited resource is sparse (battery almost empty) and then starts to care about it, the progress indicator should progress little during normal use and most when resources run out.
* If the indicator is used to indicate chances for downtime (e.g. signal strength), it should be most sensitive for high downtime probabilities.
* If the indicator is used to indicate rate of energy usage (e.g. signal strength), it should be most sensitive at the rate that is used most frequently. This may be in the upper or lower end, or in the middle.
* If the indicator is used as a provider of a value, on which the user wants to do calculations, the indicator must reflect reality in a way that is easy to interpret. For instance, if you have 5 bars for battery, each could represent 20%. Or if you have 5 bars for signal strength, each could represent a factor (constant amount of dB).
In other words, there is no perfect solution, it will always be a compromise.