I bought it at Target last night, and I asked the clerk at electronics about it. He said they got mostly 360 and Wii versions in, and both sold very well. He also mentioned the PS3 version didn't sell well, but that they didn't get too many of those in.
I'm up to hard mode, which I don't think is very shabby. My roommate and I have probably played it a total of five or six hours, and last night we went all the way through easy alternating, then played some quickplay songs. He went on to play them in normal, and I moved up to hard, skipping medium. Of course, I lost a ton, but I'm finally able to make it through a few of the songs. Of course, I haven't tried a majority of them on hard, though.