A few weeks back, GooSync (online backup host and sync agent into Google) announced support for Tasks, but it couldn't cope with the way S60 3rd Edition bundled to-dos into Calendar. That changed a few minutes ago as a revised Tasks module just went live, handling full S60 to-do synchronisation into GooSync, including categories, descriptions, etc. Seems to work well, though note that it's not available for freebie GooSync users - you need to have plumped for the £20/year Premium service.