So I resolved to take some time and try it out and see if it would be as cool as I thought. I just finished getting an example grid working last night and I thought I'd share. the attached zip contains the basic application code and I've also included the folder structure (minus all of the library files except for my hacked direct provider).
I've also posted a more detailed blog on this that you can see here. I'm not claiming that my sample is the uber exact solution. Especially not my direct provider as I've only implemented enough to make my grid example work. I'm sure there would be more needed to fully support forms and file uploads. I'm sure the great guys working on Connect will soon come out with a more complete solution supporting ExtJS on NodeJS. But until then, here is something you might find interesting. Please comment. I'd be interested in your suggestions. I'm not sure I will have time to actively maintain this direct provider and like I said, my expectations are that an official one will come out eventually.
Update: Attached download updated to work with
* NodeJS v0.2.0+
* Conect v0.2.4+
* Mongoose v0.0.2+
* MongoDB v1.6.0