Since there's no comments. I'll chime in on this. They've been available for a while. YUI2 grids was my first experience with grids, and I hated it. Way too complicated and confusing. I quickly moved over to Blueprint.

When YUI3 grids came out I gave them a try cause I'm using YUI for my front end. The new version is much more intuitive to use, and the fluid layout is great. I'd recommend anyone who was deterred by the YUI2 grids to try the new YUI3 version.