Radim Marek clocks in for the day:
The next possible source of confusion when working with time in PostgreSQL is presence of two distinct data types:
timestamp(ortimestamp without time zone)timestamptz(ortimestamp with time zone) Despite what the names suggest, the key difference isn’t whether they store timezone information, but rather how they handle it during storage and retrieval.
Click through for quite a bit of detail and plenty of examples on how to handle date and time data in PostgreSQL. And I’m still jealous about support for intervals, especially in window functions.