Hi Steve,
I am actually using two instances of SQL Express in production:
1). An actual production database for a customer-facing internet portal - running on a server
2). An ad-hoc analytical database, where I model day-to-day analytical tasks.
In my experience of managing data for Supply Chain and Sales which is not covered in SAP in a SAP-managed enterprise, performance limitations (1 gig of RAM and 10GB of data) aren't something that will make you or your boss consider a $7k cheque for a Standard edition. There are tools, such as indexed views that can help you deliver fluent ad-hoc reporting even on a large volumes of transactional data.
What made my company invest in buying MS SQL Std is the SSIS.
Best,
Constantine.