This was driving me nuts so I'm adding a note here.
Took a while to get the simple time zone abbreviation for a given time zone. If you have the name just do this:
$dateTime = new DateTime();
Will return PST
[red.: Or PDT is the current date/time is during Daylight Savings Time]
The mention of using 'US/Pacific-New' is actually a deprecated process.
See here: http://us.php.net/manual/en/timezones.others.php
Where it is described:
Please do not use any of the timezones listed here (besides UTC), they only exist for backward compatible reasons.
If anyone is confused about the US/Pacific-New that appears in the list, apparently it has something to do with a bill that was that was passed by the House in 1989, but never signed into law. It has to do with delaying the switchover until after the election. Read more about it at http://catless.ncl.ac.uk/Risks/13.87.html and it should be the first posting. Or just do a search for US/Pacific-New.