Her's some information...

In 2006, daylight time begins on April 2 and ends on October 29.
In 2007, daylight time begins on March 11 and ends on November 4. [New law goes into effect.]
In 2008, daylight time begins on March 9 and ends on November 2.
In 2009, daylight time begins on March 8 and ends on November 1.

Does this mean that I needed to disable DST (in vBulletin Options) on November 1st?

According to the manual (http://www.vbulletin.com/docs/html/v...group_datetime),

"This setting is not automatic and it will need to be changed when the timezone changes twice a year."

That's surprising - now I wonder why there wasn't a bunch of people asking about that when the time changed. Maybe it works automatically on some servers?

Or maybe most people just have the guest time set to GMT.

Disabling DST in vBulletin Options didn't change anything for the guest time. It still displays GMT -4 just as it did before. Oh well, the only conclusion that I can draw from this is that the vBulletin software looks at the host server time.