NuevaSync merges all google calendars to the local N900 calendar. I don't know if there is a chance to sync to multiple calendars. It is very reliable so at the moment I think this is the best what we have... ...
Possibly, if the phone itself supports multiple calendars. At present the only device we know with multical support is the iPhone. The service merges calendars for all other devices, including at this point the N900. We can add a special mode where we can de-merge the calendars for your account. Then you can test and we'll find out if it works. There are other devices that have native multical support, but still don't do it for Exchange sync (e.g. the Palm Pre). It would be nice if the N900 isn't like this.