It would be handy to have a way to union multiple filter's worth of results into one result set. It should then be possible to feed said union into one of the portlets such as "Show Saved Filter" or "Two Dimensional Filter Statistics".
An example user of this would be one of our development managers who wants to track results for users assigned to two seperate development groups (e.g. "Dev-UI" and "Dev-Communication" or something along those lines).
Criticality on this is pretty low but the convenience factor would be extremely high 
New Feature
Resolved
Minor
It would be handy to have the capability to "union" multiple sets of filter results 
But since I often open a lot of my own issues myself, I really want to see "Open Issues submitted by me (assigned to any team other than mine)". And I thought I could do that by defining an "Open Issues Assigned to my team" filter and defining another filter that is just ("Open Issues submitted by me" minus "Open Issues Assigned to my team").
If the query engine knew that the "Open Issues" were the same set in both queries, that could be optimized out and either cached or only evalutated once.