Having checked the Mark/Space forums as a potential source of further information, I have found that there are a lot of reports of problems with Entourage 2008 syncing. It appears that these are mainly down to the changes Microsoft have made from 2004-->2008.

The prospects for syncing a BB with Entourage 2008 (particularly with all the fields that work in Entourage 2004 to BB) don't seem to be too rosy.