OnLive is a great example of the best scenario in future gaming.
Just click Play, and you're in.
Sure, if you don't mind the downsides. Like that you are guaranteed to have the games you "buy" for a couple of years IIRC (after which they may be e.g. removed from the service, if not for other reason but that the game servers they were running on were upgraded due to newer games, hence compatibility problems have risen with those older games), and if you have the PlayPack pass to play hundreds of games for $9.99/month, I think also there they may remove games to make "room" for other games.
So basically, you could see a game you still wanted to finish some day removed before you could do so, and there's nothing you can do about it. So it may be a good service for people who just want to play "something" and hop from games to other games
For game collectors like me, it is not a preferable scenario. It is taking me even further away from being able to control the games I want to keep than e.g. Steam with 3rd party DRM. That doesn't mean I wouldn't play any games on OnLive, just like I have bought games on Steam too even though I don't really like it.
Just as with Steam, if the masses go for streaming gaming and playing installed games becomes a niche market, I guess there's little I can do about it, other than keep voting wil my wallet as long as I can. Maybe both markets will co-exists side by side, who knows.