So does anyone know what kind of VRAM usage we are talking about when you have something like MGSO running with full animated grass etc?

It would depend on the settings. Are you looking for the max? As in, fast computer with highest MGE settings and shaders?

I am just curious if the game ever really goes over 1GB of VRAM when you start maxing out grass and distant land settings.

Well, if you have most of the textures in DDS format, most wont be over 660 something kb per texture. You typically wont have but so many loaded at one time anyway, maybe several hundred at the very most; probably more like only a few dozen at a given time. Meshes themselves only take several dozen kb typically at most and you wont typically have more than 1000 at a time. If you include distant land in this, the figure for meshes will definitly go up, but considering those meshes are simplified, they wont take up much space.
So taking that stuff above into account, I would have to say that you are definitely unlikely to go over 1gb of memory usage. (its good to note that alot of resources are still required to actually display things though and a straight base ram amount is only a way to get a "feel" for something)

However, the above is only an estimate as I cant say for certain how much stuff a particular person might have loaded. Eitherway, if you have a computer that comes with a couple gb of ram, you shouldnt really have much to worry about.
I know my computer has 3gb of ram and a card with 512mb and I have replacers for almost every texture and tons of meshes and it still works fine for me.

I am talking about onboard VRAM on the video card, and i can safely say that with just testing MGSO+ 65 percent density grass, and 15 cell distance, that my two SLI 560 ti's are using up that whole 1GB of video ram. Tested it using GPU-Z.