Milo, your question about why tip-jet copters are not seen was answered: They use ramjets at the blade tips. Ramjets are, basicly, afterburners minus the jet engine in front. They suck down fuel like it was being poured down a drain.
Other than that, they were torque-less. Bearing friction would try to spin the craft around a little, but is easily countered with aerodynamic controls.
The model you saw in the lower of Falcon's pictures was a little different, though. It had a conventional turbine engine, that was used as a 'gas producer'. Compressor bleed air was ducted to the blade-tips, rather than using ramjets. The end result was the same, though the difference in fuel usage between that and a ram-jet tipped model was negligable.
EDIT: Gah, I should of read more before opening my yap... This is what I get when posting when I feel like passing out from exhaustion
