I mailed this to the Philatelic Bureau in Stanley (Falkland Islands) in December of 2009, just after these stamps came out. Guess it took a good year for my letter to make its way down to Rothera and be processed for return. It was cancelled there a little over a month ago.
Rothera is the main British Antarctic Survey base, located on Adelaide Island at the tip of the Antarctic peninsula. It is a year round base maintained by a staff of over 100 in the summer and 20 in the winter. The base has a runway and is serviced by 20 round trip dash 7 flight from Stantley each year.