I also played around with Sunbird for a while. While it is a good start, I feel it needs time to mature. If Outlook were an option for you, I would have suggested using Plaxo.
I struggled with the same problem for a while and this is the solution I have come to. I use my office Outlook with plaxo for 95% of my calendaring needs. Plaxo allows me web-based access and Outlook provides me with a highly usable desktop client. For the 5% items that are highly personal and which I would not put in my office systems, I use Yahoo Calendar. So far it has been working for me.
With due respect, perhaps you give Google too much weightage over Yahoo. Yahoo has a heapload of connected, personal information for millions of people and, so far, they have done an admirable job of protecting it and continuing to provide quality, free services.
Given the rate at which Google has been doing betas, perhaps if we were to wait just a bit we would see Google Calendar on the scene!! Here is some more
Google musing. Do post what you come up with, it would be very interesting to know of a better/alternative solution.
[ June 22, 2005: Message edited by: Sharad Agarwal ]