Wouldn't it be nice, if the number of tracks shown under the collection, matches the number of tracks found by filtering?
For example:
5436 tracks in collection
added:<8d playcount:0 will match 306
So 306 should be the number below "Local Collection" and all operations will only affect these 306 tracks, until I clear the filter.
I would use a bookmark on this filter to fill my iPod with the newest unheard tracks after I have deleted all heard tracks (playcount:>1).
Shouldn't be that hard, as MySQL returns the number of rows affected.
Btw. The ability to filter after the comment field would expand the flexibility enormous.

m0nk