Facebook database design?

I have always wondered how Facebook designed the friend <-> user relation.

Database Structure Advice Needed

Im currently working on a site which will contain a products catalog. I am a little new to database design so I'm looking for advice on how best to do this. I am familiar with relational database design so I understand "many to many" or "one to many" etc (took a good db class in college). Here is an example of what an item might be categorized as:

Object Oriented Programming: More than just basic objects

I seem to find all documentation regarding OOP too basic or too advanced. I'm trying to solve a specific problem and I can't get a nice solution without having to use Singletons or global instances or the such.

PHP/MySQL - store default text in database or in a file?

OK so I am creating a system where whenever a shop signs up, they get 10 default slides that they can then customize later. The default slide data is just a starting point for them. But I have to assume a lot of shops will not log in and update the information, they just want something up ASAP.