I've Googled the group (not exhaustively however) and can't find
any reference to the use of these 'casters' to replace miter slot
bars and was wondering if anyone has ever done this before. Also would
like suggestions for other WW applications (besides work infeed/outfeed
support) for these casters and/or comments or criticisms of my idea for
utilizing them.

Recently came into a bunch (as in lots and lots) of 'ball
casters' or 'ball transfers' or as Woodcraft calls them 'ball
bearing work rollers'. They had obvious WW applications for
large/long work support. . Woodcraft sells a flange model but these
are stud mounted with a threaded bolt out the back. Various styles are
available at McMaster Carr. In the process of utilizing some as an
outfeed support, I noticed that they set into and rolled nicely in the
miter slots of the TS. The photos here
http://photobucket.com/albums/v697/mike72903 show a simple sled that
uses four of the rollers as guides in the slots instead of miter bars.
A box joint jig I designed to utilize the sled is installed on the sled
front. The sled is remarkably stable as long as some downward pressure
is applied while pushing straight forward. There is absolutely no
detectable side to side slop and absolutely zero binding along the
length of the slots. It glides along with no effort even with heavy
pressure. The rollers on one side were mounted in slots so they would
align perfectly with the slot before final tightening. A couple of
already noted disadvantages a If you push with a twisting,
non-centered or sideways motion without applying enough downward
pressure it can come out of the slots. Also, you lose about an inch of
cutting height because the base of the sled rides above the table top.
That wasn't an issue with the box joint jig because it mounts
vertically on the front and could be lowered or raised to wherever
it's wanted. Next I'm going to make a dual slot cutoff sled using
these rollers. Probably two rows of three or four rollers spaced so
the sled will remain stable if either sled edge runs past the TS edge.
I'll see how that works. And Yes, the finger joint jig is using
metal for the spacer finger. If anyone is interested I'll be happy
to pass along my solution for the "ultimate box joint jig".