Finally! Great choices, too. I've been wanting to try three of those (and already own the fourth).

I will just keep the demos and never buy the games.

The only one of these games I'm interested in is Jett Rocket, but I'll probably try them all just because I can. Except for And Yet It Moves since I downloaded it already, and it isn't particularly compelling so the demo probably won't help sell it.

I'm glad the demos are a feature here to stay though, I'll probably try out every demo for games I don't have downloaded.

Statements like that are why Nintendo feels justified in not giving us nice services on Wii that have long since been standard for every other platform.  :@

Thrue Space is a GREAT game. It's like that hole in the wall TV show and tetris combined

Actually, I heard that the demos will be up for a month, so the updates won't be weekly but rather monthly. I don't know if this is true, though, so I may have to investigate.

I'm happy to hear this, especially for the Bit.Trip Fate. I've been curious about the series, but I have yet to try it out. 

Though part of me understands Kytim89's point (and Nintendo's, for not wanting to allow this to happen), even if 10% of people that try the demo follow through and purchase the full game, that's a huge incentive to offer these.  I'm intrigued by all four of the chosen titles, but would probably only download the Bit.Trip one (having enjoyed the previous games).  So if I try the ThruSpace demo, you're not losing a sale, since that wasn't ever going to happen.  But you're gaining a potential sale, since if I love it I might just buy it.  I know the reasoning behind demos are not some unknown science--this is more just me, thinking out-loud and trying to figure out why a company might think they're not a good idea in the first place.
Anyway.  I'm excited.  Weekly or monthly, I'll take it.

I don't think people who will download and play only the demo and never buy the game would have bought the game without the demos. Out of all the demos that have been made available, I have no interest in buying them, so even though I'll likely end up just playing the demos, there's still a possibility I'll buy a game I wouldn't have before.