Yes, I have it and I am super happy, I take it with me around the world, I got mine from the UK so it was preloaded with all Europe maps, then i bought from Garmin site the South East Asia one, it covers Singapore, Malaysia West and East, Brunei, Thailand, Indonesia (except Sumatra) Hong Kong and Macao.
The Nuvi interface is nice, but I like the details from Ohayo Zumo 500. The best feature on the 660, unfortunately cannot be used here, is the 3D maps, in Europe it is all calibrated it is really amazing for navigation.
In Singapore, I heard that they will do 3D calibration sometimes next year, so now on 3D maps, all buildings are flat.
Also with the car mount, when you plug it the GPS into it, it automatically recognizes the car and configure the unit for car navigation.
Nonetheless, it is a really good GPS unit, expensive, but top quality and graphic definition.
If you travel out of Asia, a bunch of tips and extras to upload for tours and trips from the zumo 660 US forum.