A few simple engineering questions

OK, guys...I'm finalizing my plans (5th time, I think) for a wood
router, and I have a few questions.

Z-axis. On most designs I see, there is a vertically oriented axis,
which has the spindle (usually a router or a Dremel...in any case a
non-negligible weight) cantilevered at the end of an arm. And it raises
and lowers on linear bearings. Doesn't this type of loading cause the
bearings to wear prematurely, and in a predictable pattern? Has anyone
come up with a better design...one which places the router's center of
mass between the slides, for instance? This seems to be a relatively
simple task...what's the down side to it? This graphic,
<http://www.cnczone.com/attachment.php?s=&postid=3691> is perhaps the
best one I've seen, to illustrate this cantilevering. Is this a problem
in real life? Theory says it should be...but theory sometimes
complicates things unnecessarily.

Y axis. I've decided to place the rails next to each other in a
horizontal plane...mass of the Z axis centered between them. I
understand that this type of layout is used in the ShopBot, and the
ShopBot is known for Y axis flex. Is this a function of this type of
design, or is it just a problem with underspecced parts?

Antibacklash nut design. While this is far from a commercial grade
antibacklash nut, it seems that it could be implemented by using off the
shelf PVC as an adjustable spacer, between 2 tapped nuts. In fact the
whole thing could be implemented by tapping the PVC, but I would doubt
the material's longevity in use. Take a female threaded cap and a male
threaded plug...screw together. Drill holes in both ends and epoxy nuts
to the ends. "Dial out" backlash by using the threaded
couplings...since the thread pitch for the fittings and the lead screw
are different, adjustment will occur. And, if the fittings slip in use
it's an easy matter to add a set screw. This seems to be a workable
design, and one which *anyone* could build *without* machine tools...but
it seems too simple. Comments? Surely I'm missing a detail, somewhere...

I await your responses.

-- Chuck Knight