Neil McFarlane submitted this to discuss:

See the attached mockup.

I'll explain some of the functionality that I'm not able to present adequetly in the mock-up here.

1) The options within the "attribute" selection box are populated based on the selection in the "entity" selection box.  The current selection reflects options that would be present with the entity-All option selected. 

2) The "help" link above the condition text box creates a pop-up that tells the user how the formatting works (ie. how +, -, , : etc. are used.)

3) Pressing the "Add" button moves the condition(s) into the criteria box.  Multiple conditions can go at once.  In the example shown, it would have been "+foo -bar" with the entity selected as "Forums" and the attribute as "title".

4) In the criteria box, the red X deletes a condition, the little pencil brings it back to the left part for editing.

5) In the criteria box, the third column can be either "+", "-" or " ".  Clicking on the cell/location alternates between the three.

6) The way I envision the search to work would be that it would bring back all results matching applicable criteria.  For example, in my shown search, it would bring back forums matching the forums criteria and documents matching the document criteria.  Other entities would not be returned.  If the "all" entity is used to set criteria, then entities must meet both their specific criteria and the general all criteria to be returned.

7) Although they aren't shown, the critria box and results table would each have a scroll bar attached to them.

8) The and symbols represent expanded and collapsed respectively.  For example, this means that the "Advanced options" can be collapsed.