The trouble with this approach (as you may be aware :-)) is thatif the board farm includes a few 'rare' board types that happen
to be covered by a broad system property criteria used by most
people, it can be tricky to schedule jobs which really require
the 'rare' board type, because the rare resource can get
monopolised by a big job which could have run on anything but
happened to get scheduled to the rare board because it was
temporarily free. This is particularly acute if the rare board
is also a rather slow one.