Just like Confluence has the ability to create personal spaces (that are driven off of the user's username), it would be really cool if users could also have their own Personal Projects in JIRA.

The user should be automatically added to the Project Admin role of the project.

Project keys using the user's username is a safe bet since they should be unique within an instance.

I have had several requests by users to create projects, with the project key being their username, so they could keep a list of to-dos and such of their own. And then sometimes those issues get moved into the shared projects.