O2 helps with reading the patterns, but not with learning the controller, and how to play some stuff. And scratching makes it pretty different as well. I've had well over a year's worth of O2 experience (I used to pwn you at one time MilkChan... God I miss those days), and it's not helped me much with IIDX.
Even with say, 80 songs in a game, if 40 of them are below say, a 6, that makes half the game way too easy for me to even play, which cuts the number of songs I'll even play to 40. I'm used to having around 600-1200 songs in stepmania, and anything with less than 600 songs or so makes me feel practically trapped by the selection.
Which reminds me. I need to download stepmania again. Fuck I hate having to reformat.