CF does take time to start, but as I'm sure you realise most of us hibernate or suspend our systems rather than shut down.
I've just done a cold start on an unoptimised xp install with CF and a lot of background applications. 63secs from ignition to video playback which includes bios lag due to a dodgy usb device.
Out of hibernation, from ignition, to CF playing video 32 secs again with bios lag.
Those times aren't fantastic imo and needs optimisation plus the USB issue sorting out... Also I've got a SSD on order which will speed things up.
I'm going to test windows 7 on the ssd too, maybe that'll speed things up in terms of hibernation times.
I had a Kenwood double din prior to my CarPC and the time from ignition to mp3 playback was 27 secs so I'm happy with the above results!
IIRC with optimised xp on a fresh install I was getting closer to 25secs from hibernate.