I have a presentation I've given a couple times related to metadata and extended properties:

http://code.google.com/p/caderoux/wiki/LeversAndTurtles

Using it to fine tune code generation so that code can be re-generated without re-applying manual tweaks is very powerful. You can also use it to manage system self-tests.

I have applied to give this talk again at SQL Saturday in Pensacola and Baton Rouge.

Adding some layers of utility functions and views can help to simplify the awkward "API" which SQL Server provides. I liked this article, because it gave a good indication of the problems with "levels". In my shell API, I wrapped the levels with dotted identifiers (schema.table.column) to make things more uniform.