I think the section on "Date's time zone" is wrong at http://drupal.org/node/1455578
I would edit the page myself but I don't know what the intended behavior is. The page says "When the date is saved to the database, it is not converted & the time zone information is saved with the date. When retrieved from the database, no conversion is performed and the date is displayed exactly as entered."
In fact it looks to me like some conversion is performed, but I don't understand the rationale behind the conversion. On my site I entered 18:30 for the start date of an event, but if I dump the data I see...
["value"]=> string(19) "2012-08-07 23:30:00"
Whereas if I set a date field to "No time zone conversion" and enter 18:30, I get...
["value"]=> string(19) "2012-08-07 18:30:00"
So it appears to me that the documentation is correct for the "No time zone conversion" section, but not the "Date's time zone" section.