What every programmer should know about time
> Timezones are a presentation-layer problem!I want to correct this common misconception that UTC is enough. Calendar time with all human traditions involved is more complex than a simple timestamp.The advice above is incorrect for calendar and scheduling apps, or anything that has a concept of a repeating event.An example: we have a weekly meeting occurring 9AM Monday in San Francisco. You are in London and want to attent the meeting over Skype. When is it in London time?It depends.On  7 Mar 2011 it's at 5pmOn 14 Mar 2011 it's at 6pmOn 29 Mar 2011 it's at 5pmTo make these calculations, you need to know timezone & daylight saving time (DST) rules of both your current location and the home location of the event.A "DST zone" of a home location of a repeating event has to be saved together with a time and thus it's not just presentation-layer issue.