I've been thinking about this one for a while and I think it would be a good one.

I know you can create your own workflow with your own status in Jira, however, I bet everyone is always interested in knowing what tasks are blocked or impeded by an obstacle... specially one group in particular, care to guess?, yes: Management

Management (under the Theory Z at least http://en.wikipedia.org/wiki/Theory_Z) should always help developers/employees with obstacles, which can be things such as: awaiting customer/user response, fuzzy requirements, etc.

Having this in the default Jira workflow would improve the user experience and make Jira more useful.

Rally is an issue tracking system that has a blocked state built in, and users do take advantage of it.