I work with events in many different timezones. I find it a little difficult to select the timezone for an event in Kalendar. I prefer how Evolution does it, with the selection of a point on a world map. Otherwise, having the possibility to filter the list by a search would be nice. Another option, if we could save some timezones as favorites and have that at the top, that would work well too.
I was also surprised at how bad the UX for selecting a timezone is - "search as you type" doesn't work, so one is forced to scroll through the whole list manually. It seems like Timezone support was added as an afterthought and none of the developers actually use it. KOrganizer suffers from the same problem, but its Templates feature lets you save a preset which uses the correct timezone.