My Rants and Raves about technology, programming, everything else...
Ok, this pet peeve is a biggie. Over and over I have seen database schemas that simply defined the table structures and some stored procedures. Most modern database systems support advanced features for maintaining database integrity.
If you are going to go through the trouble to define a database schema, please finish the job. The database will help you do your job if you simply define Relationships, Constraints and Triggers. There are good tools for helping you do this. I really like ERwin or Visio for designing databases.
The most common error I see in badly scalable database code is reckless use of the connection object. For all multi-user database programming (which accounts for most of the work these days), database connections are a limited resource. Don't let it be your code that is hanging on to his connection way after you are finished with it. I am *not* saying that all work can be done disconnected. I am simply asking you to keep in mind that Connections are precious things. Try to do these two things: