GPS doesn't, but GLONASS does:

  GPS Time is designated as being coincident with UTC 
  (USNO) at the start date of January 6, 1980 (00 hours). 
  GPS Time does not count leap seconds, and therefore an 
  offset exists between UTC (USNO) and GPS Time (at this 
  date in April 2007: 14 seconds).

  Unlike GPS, the GLONASS time scale is not continuous and 
  must be adjusted for periodic leap seconds. Leap seconds
  are applied to all UTC time references as specified by 
  the International Earth Rotation and Reference System
  Service (IERS). Leap seconds are used to keep UTC close
  to mean solar time. Mean solar time, based on the spin of 
  the Earth on its axis, is not uniform and its rate is 
  gradually changing due to tidal friction and other 
  factors such as motions of the Earth's fluid core.

http://webone.novatel.ca/assets/Documents/Papers/GLONASSOver...

This is the best overview I've seen of all the pros/cons with regard to UTC and whether leap seconds should be abolished:

http://www.agi.com/downloads/resources/user-resources/downlo...

Basically, much in the same way that we all despise DST (or date differences between Julian/Gregorian calendars), a certain part of me wants to know, if we humans last on this planet long enough, that our descendants thousands of years from now won't look back and curse at us for being idiots and deviating from celestial time.

A lot of RFCs, the first that comes to mind is the timezone seconds offset in DHCP replies and time fields in openpgp standard.

Google probably knows a lot more:

  UTC site:rfc-editor.org