ha ha :-)
i know this is lame, but up till today, i had never actually tried in-car turn-by-turn GPS for myself :-P
that changed today, when the need to travel to Republic Polytechnic from Holland Village presented me with the perfect opportunity to try out Mobile Maps South East Asia from Sygic :-)
to my pleasant surprise, the iPhone found the requisite satellites pretty quickly from the open-deck of the Holland Village carpark. the voice-directions were clear (i chose the British English voice) and the various bits of information (speed, relative proportion of distance covered, lane-assist, estimated time of arrival, etc) were nicely laid out onscreen.
i think the way the speed-limit of the road one is presently travelling on is dynamically updated, together with a warning if one is exceeding that limit, is especially cool and useful.
i used it again on the way home, after the visit to the polytechnic. it didn't seem to drain the iPhone's battery all that much.
oh, and it recalculated the route quickly too, when i deliberately took a wrong turn :-P
i love it :-)