DateBk5 for PalmOS gets this right - which is why I use it for calendaring, and only every use the Mac (or really any other system) for reminder popups and occasional data entry wrt schedules.

Simply, an event is *either* in a given timezone *or* in "local" time. The particularly good case for this is "oh, the california office is doing a conference call at 10am... and as usual, they mean their time... no problem, click click, scheduled for 10am pacific, oh look that's 1pm here, great." Another way to think of it is "reminders for *me* are often local; reminders about *other people* are usually anchored." It's only one small feature, and there are a few hundred other reasons I use DateBk5, but this is the issue you've brought up...

Apparently chronosnet has a palm-oriented Mac PIM suite that actually supports the pimlico datebk extensions, too, but I haven't tried it yet.