rack&pinion

Hi,

Excuse me for going in a different direction as everyone here seem to
be fixed on ball-screw or its poorer cousin the lead-screw, and would
thumb their nose at rack-and-pinion, but.....

Questions:

Why? Is it because of higher backlash? If so, any qualitative
indication? Any redeeming factors? (like higher speed, easier
construction, lower cost?)

How would one keep the "pinion" on the "rack"? Any link to a site for
more information, especially diagram?

Thanks

Peter