Yes, I am very disappointed with Nokia and lack of bringing out an iSync Plug In for the N97. I'm currently running on v12 firmware, and the new version is due out next month AFAK ( v2.0 or some folk call it v20 )
Hopefully, that might cure the iSync issue and Nokia will then bring out their plug in.
However, there is workable solution with the N97. If you haven't got one yet, get a Google account.
You can then sync the Mac to Google, sync the Address Book, and sync iCal to Google Calendar. So there the two calendars and contacts can sync with each other.
The next stage is then to sync the N97 with Google, this is done via Mail for Exchange.You will need to download MfE onto the N97, and then set up a profile, which allows calendar and contacts to sync with Google, and then these will also reflect back onto the Mac.
Now I have it set up, it's working quite smoothly. THere is then Nokia Multimedia Transfer and this can connect to the mac via Bluetooth for transferring audio / images ( doesn't seem to work with mine via USN connection )
THere is a longer and more detailed set of instructions, will post up the link if needed.
cheers.