I enjoyed being able to add metadata to a connection in Microsoft SQL Server. I’d annotate my connections so that a DBA could learn a little bit by inspecting it. For example, what was its purpose, and from which application did it originate? The employer where I did this wasn’t perfect at managing their database user accounts and so forth, and there were many servers with hundreds of databases on each server, so this was a good way to provide some extra hints.
That hasn’t historically been available in MySQL, but with MySQL 5.6, it will be. This is a nice addition. I assume the support for it in the connector libraries will grow over time.
I used to emulate this feature in client-side code. That workaround is still in useful production deployment at a previous employer.