I think there should be a date and time (and timezone) configuration capplet.

 1. UI must run as the user and not require privilege
 2. should not store date, time, or timezone state but take them directly from
the system so that command line tools will still work correctly
 3. must notify the system of date and timezone changes
 4. should allow the distro/vendor/sysadmin to use their own authentication system
 5. must be written in C (particularly the backends possibly running at higher
privilege)
 6. must provide a mechanism for the distro/vendor/sysadmin to lock down ability
to change settings
 7. must support multiple platforms
 8. should not hard code vendor version capabilities

The date configuration in gnome-system-tools and system-config-date in Fedora
fail on many of these points.  So, I decided to start from scratch - kinda.

The design is as follows.  A capplet written in C that acts as a shell for
GObjects gnome-date-selection and gnome-timezone-selection (modified versions of
gnome-date-edit and e-timezone-dialog).  The shell populates the timezone by
calling supplied program, gnome-timezone, synchronously.  The date is obtained
from localtime.

The gnome-timezone-selection uses libical (via e-d-s/libecal) internally to get
timezone information.  The interface uses Olson timezone locations for
getting/setting.  The interface for gnome-date-selection uses GTime.

To set the timezone the shell checks if the timezone is locked down and if not
runs asynchronously: 
GCONFKEY_AUTH_CMD GCONFKEY_TIMEZONE_SET_CMD "timezone"

Where, GCONFKEY_AUTH_CMD is an optional authentication mechanism, such as a
graphical sudo/su.  GCONFKEY_TIMEZONE_SET_CMD is the command to use to set the
timezone, and defaults to gnome-timezone.  A distro/vendor/sysadmin may set the
binary setuid or use something like consolehelper in Fedora.

The supplied command gnome-timezone tries to identify all the ways the timezone
is set on a system and then changes each one.  For example, if the command finds
a timezone set by /etc/sysconfig/clock and /etc/localtime, it will change both.
 It does this by checking capabilities rather than checking OS version.  This is
in contrast to gnome-system-tools which only supports a hard-coded list of vendors.

After the timezone is set successfully, a message is sent on the system bus. 
This can alert processes, such as the clock applet and evolution, to update
their timezone settings.

The capplet UI listens for this message on the system bus to update itself.

Setting the date works similarly.  gnome-date simply parses a standard ISO date
format (in localtime without specifying timezone) and calls settimeofday().

Patch to follow.  Please let me know what you think.  Thanks.