Sometimes it is helpful to look for issues in Jira that have certain relationship between other elements in other Atlassian products. For example, doing a search to list all Jira issues that do not have a Crucible code review associated with them. As I understand it this is not currently possible.

Where one of the strengths / selling points of Atlassian products is their integration with Jira this seems like a logical extension to the current JQL APIs.