I too have developed my own database for my collection.  Mine is a web
front end on top of a relational database.  I did it this way because I
hardly ever use a Microsoft OS and wanted to learn how to build a web
application.

One of the best features (I think) is the ability to export the database
onto my PDA.  That way I can have it with me when I'm away from my
computer.

If there are enough developers interested, I could make the source
available for others to help.  One of the big features I'd love to add
is multi-user support.

Jeff