Each platform instance has a Time zone.
The default time-zone is AEST (+10), which is a day-light saving time zone.
You can change the time zone of your instance by opening ‘Settings’ in the Control Panel.
All dates are internally stored and manipulated in UTC (+0). See: http://en.wikipedia.org/wiki/Utc.
All controls will display dates in the local time zone, and treat dates entered as local dates.
The Formula evaluator will show resultant dates in UTC, and VAR_DUMP will do the same. This can be confusing as you might see a midnight value as 13:00 or 14:00 the previous day.
Time zone dependant Formula functions
Any formula function that is time zone dependent will use the current time zone; E.g. TODAY(NOW()) will get you a date time representing midnight of the current local day.
Time zones and Conversion
Dates in a particular time zone are often depicted as e.g. 12-Dec-2013 14:00 (+11) where the time zone offset is +11.
In such a situation, to get the UTC date you simply subtract the time zone offset from the date and you will get the same date in UTC
localTime = 12-Dec-2013 14:00 // at +11 utcTime = localTime - 11 hours = 12-Dec-2013 3:00
localTime = 12-Jan-2013 00:00 // at +10 utcTime = localTime - 10 hours = 11-Jan-2013 14:00
Daylight savings (See for Australia: http://en.wikipedia.org/wiki/Daylight_saving_time_in_Australia, for other countries: http://en.wikipedia.org/wiki/Daylight_saving_time_by_country) makes this a bit more complex.
In AEST we alternate between a time zone offset of +10 and +11 depending on the time of year. (We have the DST time zone offset of +11 from October to April)
We recommend not worrying too much about UTC vs local time when not absolutely necessary. Most calculations are not time zone dependent.