What are the tangible benefits for using KDE or RoxBox or other alternatives to the Hildon interface?

Is it primarily so you can run non-Hildonized apps?

I had a Zaurus at one time, and I found that using the alternate window managers was cumbersome because of the relatively small window widgets that had to be manipulated via the stylus. I would imagine on the N770 or N800 the difficulty would be very similar.

You'd think they'd (Nokia) have some kind of wrapper that could run anything within the Hildon UI so people wouldn't have to boot into an alternate window manager, or rewrite apps. Hildon should intercept the standard UI functions of X apps so developers wouldn't have to port, just recompile.