In our applications, we use Access based Personal GDB files to cache data in order to limit network read/writes and also improve performance by doing processing locally. The best thing with Access was ability to use Jet OleDB provider and ADO.Net to read/write and do complex math on our data. That way we are not limited to use relatively slower and limited functionality ArcObjects. However, the problem with Access is the delay in flushing data. We would insert some data to a table and sometimes this data would not be flushed to the mdb file, hence immediate reading of the table would not return the just inserted records.
As we are investigating other options, I liked the idea of file based gdb in ArcGIS 9.2. However, the limitation is inability to use ADO.Net Oledb provider to access data. ESRI Oledb provider can be used for reads (no inserts and deletes), but there is no documentation if it supports file based gdb. My wishlist for ArcGIS 10.0 would be for ESRI to extend the ADO.Net Oledb provider and give native access to ESRI geodatabase data.