Me thinks in November.

I swear I read somewhere that this was also being released on the DS. If so, then I guess they changed their minds.

The PS2 wins because of all the PS2 guitars out there from GH2. On that logic the 360 should come in second, but I think there's a chance the Wii version beats it out. How the guitar controller intereacts with the Wii mote will be interesting. Here's my total sales predictions.

1. PS2 1.8 million
2. Wii 1.0 million
3. 360 .9 million
4. PS3 .6 million

Guitar Hero, huge casual game. If Wii gets a hard-drive for downloading songs, then it should do better.
GH2 for 360 went out this year, many 360 owners won´t buy GH3 when they have just got GH2 or can get it cheaper. And for what I´ve heard GH2 guitar isn´t compatible. If it were, then PS2 and 360 should be the best selling version. Anyway, here is my prediction:

PS2 >>>>>>>>> Wii >> 360 >>>>>>>>>>>>>>>>>>>>>>PS3.

Wii and 360 sales depend a lot in my last arguments.

Due to existing GH hardware in the market and the size of NA user base I would say

360>ps2>wii>ps3

Though, if enough people upgrade this year to nexgen machines then

360>wii>ps2>ps3

I have never owned the game, but I am considering it for the wii.

Are there 2sku's for the game, one w/ the guitar and one w/o?

There are just way too many PS2 consoles out there for any of the newer systems to compete with. Add to that the strong fanbase and install base of guitar hardware, and it's hard to imagine any console beating the PS2.

I'd say PS2.

Everyone's already got the guitars.
Then 360, because...same reason.
Then Wii because there's so many users.
Then PS3 because it's got the smallest userbase.

We've seen many times lately that multi-plateform games debuted better on 360 than on PS2 (the last to date is Spiderman 3) so I won't be surprised to see the 360 version taking the first spot.
I also think that the PS2 version will come 2nd. Sure Wii is selling great, but the installed base of the PS2 (and all those who bought GH I&II on it...) is still big.
I also except this holiday to be the last one we see PS2 games on the top.

PS2>360>Wii>PS3