I just tried my collegues Garmin Nuvi 310 which he has kindly loaned me for a couple of days to try out. It has a flip up antenna and the initial lock to the 4 satelites took ~5 mins as I was driving (Vkool tinted). Usually it takes less than a minute according to him, but it was raining, cloudy and we were moving. Once its locked, it picks up the signal quickly even after lunch once we drove off from the basement car park, it was only a matter of seconds before the unit found the satellites. The lock process will be required again, once the orbits of the satellites change (usually each day).
Beyond that, the unit is marvelous, and the mounting bracket to the windscreen is nice and tight, no rattles and it looks good as well. Easy to navigate, and from what he said, the malsing maps installed on the unit is the one to have for Malaysia and Singapore and its much more complete than even what BMW Malaysia is offering on the GPS Navigation DVDs. Also Garmin is the most user friendly unit there, very well thought out.
So far, my take is that the Garmin Nuvi unit is a really nice unit. If only the price drops a bit more... lol