Hah! One of the most significant design problems with Windows is how it handles time. Its internal clock is based on local time, which means that its internal clock jumps by an hour twice a year (in places with Summer Time). And its time zone tables can only hold two different set of time zone rules. And this includes Exchange. When the US time zones changed last year, cross-zone meeting times were screwed up for weeks.

In summary, how Windows deals with time blows.