I just called Garmin support in the UK as both my GNS430 and my 196 are WAAS enabled and I was curious. They told me that the WAAS satelites are not available in Europe yet but following the apparantly highly successful implementation of WAAS in NA we are likely to get our own WAAS satelites soon.
The 2 WAAS satelites in Geostationary orbit for the US will transmit the signal to any WAAS capable device, however as with GPS they are line of sight and we can't see them very well in Europe.
WAAS works by timing corrections that are made at specific ground stations which is then transmitted onto the WAAS capable device from the satelites which then corrects the timing.
It is the building of these ground reference stations in Europe that is underway at the moment. The corrections from the US stations are useless as they are too far away and therefore would not elliminate any of the timing errors.
So your reciever will benefit from WAAS but not in Eurupe YET!
The service is pretty good and my 196 picked them up without any problems on my last Florida trip.