My perspective is as a person who travels frequently and changes time zones several times a week. While not everyone does this, and it seems many developers never do (oddly, even at M$, given their historically unusable handling of time zones). It is, however, not uncommon.

This is a peeve of mine I've been trying to get sorted out for years. I'm not alone either, at least one rant has been cross-posted. The gist of the problem is embodied in the following:

You are in California on the phone with someone in Boston planning a phone conference from 10:00-11:30am for next week at which time you’ll be in London. What time should you set the conference for? Can you do the math? How about if you’re in Phoenix in April? There are 31 time zones and almost all contain some regions that observe and some that do not observe DST. This is the sort of irritating arithmetic my computer should do.
Time zones are actually very easy to handle - and it is also easy to give reminders to people as to what time zone they are in all in one simple modification to the "new appointment" and "new task" dialogs: just add a start and end time zone for each that defaults to the current time zone the computer is in. Why both start and end? Because when you get on a plane you very frequently start in one time zone and end in another and airlines give you takeoff and landing times in the local time zones.