I recently started using SyncMate for synchronizing my OSX Address Book and iCal with my Google account, and it works great, MUCH better than the related built-in OSX capabilities: using built-in OSX functionality, Address Book cannot sync birthdays, and iCal cannot sync "on my Mac" calendars, forcing you to cumbersome workarounds. SyncMate worked straight from the start instead.
The only missing piece for my needs would be synchronization between iCal todo's and Google Tasks.

One big problem in SyncMate, at the moment, is how the Autosync feature works: it is not a daemon running hidden in the background. You have to keep the application open, and its window pops up and its dock icon bounces for a while every time the automatic sync is started! Very annoying. At least the window is not brought to the foreground, luckily.

Tech support kindly responded in a few days, promising that they will improve Autosync in future releases. Let's hope this happens soon.
They also will investigate on a problem I'm having with Autosync no starting anymore sometimes after putting the Mac to sleep and waking it up again.

A much needed tool, thanks!