I’ve been using GooSync for well over a year now to keep my Palm Treo’s calendar in sync with my Google Calendar. It has worked very well. There are very few limitations and the syncing is fairly quick after the first time. I use the paid version and keep a two-year window in sync at all times.

I did have some trouble with the Contacts sync function and stopped using it. However, if they can manage to make that work with Google Contacts using the new API, I’ll try it again.

I have not yet tried the task syncing function.

Overall, this is a nice solution for someone like me that uses Windows, Mac OS X, and Linux and wants to keep everything synced up with a mobile device.

I use MilkSync to sync my tasks from my phone to Remember The Milk. Remember The Milk can export a calendar so you can see the task items in your Google Calendar.