EASA's consultation NPA 2009-02b, Section IV (Instruments, data & equipment), page 41, OPS.GEN.400 (c) (1) - in the context that instruments not approved by Part 21 may be carried on a flight states "The information provided by these instruments or accessories shall not be used by the flight crew to comply with (a)." (a) refers to equipment which will enable the flight crew to determine the flight path.
This seems to mean that if you carry a GPS that is not Part-21 approved it will be illegal after 2012 to use the information from it for navigational purposes! We may think that carrying a GPS is a step forward, the authorities do not seem to be convinced unless it is priced out of our range.