Let's complicate things a bit.
Before i thought USB mode is not availables in RockBox at all and relied on original firmware bootstrap for it, same as for charging.
But some weeks ago i suddenly discovered that RockBox can act as USB drive! (Pity it can't act like USB speakers, IMHO that could be killer thing. Play muic from X5 onto X5 :-) )
So, for me - it works, and it seemed (but i ain't sure, i'm a very newb to RB) to start working at about the time fix was into SVN. Still works.
X50 60Gb, purchased about last spring (i remember X5L/20 were in shops but X5L/30 were not), can put my s/n but don't think it counts.
OSes are WinNT 5.1, 5.2 don't remember of 98SE/ 5.0 / Linux (i guess i did not attached it), though can check them.
HW is i855GM (notebook) for 5.2, SiS 761 for 5.2.