When I use IN-A, and select SHIPMENTS,  BOM,  WHERE USED, or any of the buttons that bring up a list of part numbers, I have an almost uncontrollable desire to hit return on one of those items in the list and have it redisplay the IN-A screen with the selected part number.
 
As an alternative, it would be cool if pressing return would save the part number selected in some kind of local variable that could be pasted into the part number field on the main IN-A screen (maybe by pressing enter on a blank Item Number field??).
 
Just some random thoughts.

Let's not be so quick as to lump this into the all elusive, ideal 'Drill down capability'.
 
The second example I gave would just provide a 'scratchpad' to hold a copy of an item number so that it can be called up on the main IN-A screen.  
 
Some would say 'why bother', but my position is that something that could be implemented quickly like that is Infinitely superior to me keeping this scratchpad and pen next to my mouse to write down item numbers!