This is 2008. Why in the world does WordPress not know how to shift it’s internal clock when Daylight Savings Time starts or ends? If the server itself can do it, why can’t WordPress? Heck, my VCR can even automagically adjust by an hour twice a year.
I was going to write a plugin to do this, but Kimmo Suominen has already done it. In February 2005! Matt Mullenweg or someone at Automattic, send Kimmo a check for a few hundred bucks and incorporate his code into the core WP system for 2.5.
The plugin is available at Time Zone plugin for WordPress.