Not an informative reply, I'm afraid - I'm in the same boat - the multiple calendar feature on Outlook 2007 is fantastic, but near useless to me if I can't synchronise with my Windows Mobile Smartphone. (WM 6.0 using Active Sync 4.5 - Windows XP)
My Outlook set up is as follows: I have two calendars I created myself (stored in local folders), the default calendar which I don't use at all, and three subscribed google calendars (read only).
During the course of this morning synchronisation is getting worse - Initially only the default calendar would synchronise; then it only worked in one direction (PC to Smartphone), now it's not working in either direction!
A related problem is that the default calendar copies information from the two local folder calendars, creating duplicate appointments.
It's all a bit disastrous really - input from someone in the know at Microsoft would be appreciated - I've tried MS help and a number of blogs for a whole day to no avail :-(
Daniel