I went from 3.0 -> 2.0 once, no problems.
none, nada. Works fine (albit some of the included games no longer ran... probably just built against newer libs)
The Cradle, being mostly worthless DOES have ONE redeeming feature; a integrated JTAG to parallel converter.
Bricked your GP2X?, with the right software and the Cradle you can unbrick as you like.
Still I think the whole post above may just be F.U.D.