What is the best PIM software in term of ease-of-use, portability and sync functionality ?

From comments:

I would like to find a good manager personnel that match as many conditions as possible:

Working on Windows / Mac / Linux
* Work on a USB stick
* Being able to synchronize between the computer / USB / pocket PC
* Ensuring good backup feature
* Providing a robust data encryption
* Storing data in a format interoperable

The best way is a combination of the free Plaxo.com service, Google Calendar and Mail applications, and the free native applications on each platform to view offline.