OK, spent the night with the Ion Kit.
Feels great...but really have to resist comparing it to other e-drum kits, as it comes up short in so many ways. That said, works damn well for Rock Band, and I was able to set it up as I would a proper kit.
I used the two cymbals for a HH(yellow) and a Crash(green), and cheated the blue up a little so it gave a little more feel for the ride. I sat the crash over the yellow tom, and had to reteach myself to move towards it instead of the green floor tom. I'm still working to get that.
The bads have a beautiful feel to them, and bounce back perfectly. It's unfortunate that they don't have active rims..the hard rims are very jarring when hit. The cymbals (as well as the pads) are cleanly responsive. Trills, flams, and rolls come off without a hitch.
A few negatives. The pedal is superior to the Rock Band one, and superior to any simple mod, like the megapedal...but I'm surprised they didn't go with one that gave more tactile feedback. They don't have to go all out like the Omega Pedal, but there are systems that give a more proper hammer feel. As it is, it just feels like a really nice Rock Band pedal (because that's what it is).
If you set up the kit like a real drumset instead of 4 evenly spaced pads (and you almost have to, if you're going to drop the money on it) then, yes, those songs that have yellow=snare sections are broken. I know I've bitched about this before, but wow, is it jarringly evident when you play. Limelight is a great test of this. Most of the song plays so beautifully on the Ion kit, but the yellow=snare sequence simply does not work.
Finally, the feet suck. Well, the stand is all around pretty crap, but that's mostly when compared to other e-kits. The feet, however...they suck no matter what you compare it to.
All in all, if you have the money to spend, it's certainly worth it. Do know that once you get used to playing on it, it'll be very, very hard to play on the standard pads (or GH's, for that matter). Also know that you'll be choosing Hard on a number of songs just to avoid the 'issue'.