Correct, the database files are portable across all supported operating systems. There are minor differences in the UI between platforms in order to behave like a proper native application in each environment, but the data files are universal. Some data in the file that's dependent on the screen resolution (like column display widths) is stored twice: one setting for full-size desktop screens and another one for portable device screens, so you don't need to resize everything to see the data comfortably when moving the file back and forth between systems; you see the display as you last configured it for a screen of that size.

The file format actually hasn't changed at all for the 2.0 release. I even put off implementing a few features, because I want to make sure that anybody still using the Zaurus version of PortaBase (which isn't getting updated) gets the option of using an updated desktop version which is still compatible with their PDAs. A future PortaBase release will increment the file format version again in order to add new features, at which point the older Zaurus version won't be able to open files created or modified by that new release.