I try to do at least some basic documentation for my DBs. I put a description on all non-intuitive fields, and I use structured headers for all stored procedures and functions (including summary, author, date created, change history, etc.). It would be nice to have this information available in a popup when hovering and it would be nice to have that info automatically included in documentation output.

For example, we use the SQLDOC tool from RedGate. It a nice utility and it includes the field descriptions in the documentation output, but it would be nice to have the stored procedure / function summaries and parameters descriptions included as well. Having a documentation tool built in to the software instead of having to buy a third party tool would be nice as well.