what is my personal data storage as opposed to program storage  and how can I reduce it?
Program storage is the amount of space taken up by the actual app, i.e. the APK size, personal data storage is the space taken up by your personal data. I.e. if you have a to-do list program it would likely create a database and all the to-do are added to the database which would take up personal data storage space. 

The only way to reduce personal data storage is to clear the app data, but this will delete all your personal data for the app, i.e. settings and based on the example above all of your to-do's. 

What I tend to do is go to settings > applications > manage applications and then go to the all tab. Then on the menu go to sort by size and clear some of the apps near the top that take the most amount of size that aren't a big deal if I lose the data. Google Maps is usually one that takes a lot of personal data storage space. 

Hope this helps