Some places will demonstrate it and let you try it out, but that doesn't happen too often.
I got my Wii on opening day, so it wouldn't matter since you can't try out a product before it's release.
It's really fun, and is the best to invite people over to play with. And is the most reasonably priced.
$250 = Wii Console, One Wii Mote + Nunchuck, Wii Sports
And it's completely BC, anything your Game Cube did, it can do without buying extra junk.
The VC is neat too, $5 is a lot it's totally worth it for classics like Mario and Zelda.
Besides, there is nothing that the PS3 does that the 360 doesn't do better. SIXAXIS is lame in all of the games I've seen it in.