Some time after I got my HTC Hero I got presented with GTD. I then started to try to figure out how I was going to manage my tasks and calendar. The calendar part was pretty straight forward and easy to figure out. Google Calendar on the phone and Google Calendar Sync on my work computer for synchronizing my appointments.
The task part was a bit more difficult. I wanted to use Outlook at work since it is actually a pretty powerfull tool, but I didn't want to use it at home and for my private stuff.
I then remembered that a couple of years ago, I tested something called Remeber the Milk. After some testing I thought that it might a be possible to synchronize it with task in Outlook. I didn't have time to try to develop some synchroniziation plugin for Outlook, so I started Googling "plugin outlook RTM" etc. I then stumbled upon SpringxCRM OutlookSync and it seemed like it was just the software I was looking for.
I have been using it for 2-3 months now and it suits my needs quite well. There have been some issues when synchronizing large amounts of tasks (slow sync), but it gets synced and thats what matters to me.