I'm a little iffy. My X360 atm is only used for two things. Movies (netflix) and FPS games.
On the one hand Natal seems like it could be an awesome way to control my X360 to play movies. 'Start Netflix', 'Play Star Trek', or swiping my hand from side to side to search through the library and selecting which movie to play. Although when the X360 is turned off it seems like ill still need my controller to turn it on, which probably means i'll habitually still use the controller to navigate NXE.
On the other hand I find most motion control schemes for FPS games _repulsive_, especially the type that might be done for Netal. Using an air gun to shoot with, playing on-rails. It'd be enough to make me ditch playing FPS games on X360 altogether. Then what good would X360 be at that point when PS3 gets native netflix support?
There is another thought i've had for a little while. Natal is an add-on. So will there be games which _require_ Natal to work, I wouldn't think so. If Natal isn't _necessary_ to play certain games, then will it ever move past the niche audience? If certain games require Natal, then there will be a split, those games that don't use Natal and those games that require Natal.
I'll leave those who argue about 'casual' vs 'hardcore' games to other people.