I worked with ACR 5.2 as a complete editor, the goal being to evaluate how well it works "raw to final screen image" without ever invoking PS. The good news is most of the pieces are there; the bad news is the UI is lacking, and a couple of key pieces are missing.
My preference is to size screen images at 800 pixels either vertical or horizontal, depending upon the image orientation, and often I choose an arbitrary crop ratio. The first obvious problem in ACR is a lack of presets for various pixel (or inch for that matter) crops. And it needs a max. pixel setting for arbitrary crops. I did find that I could work with e.g. a 600x800 setting, and just spin it to go from landscape to portrait, some relief anyway (any one custom setting is persistent image to image).
I set the Output Sharpening to 86ppi (19" display 1280x1024) and evaluated the screen/high output sharpening. It works well, no halo on the final image but a nice crispness; had to use the eyedropper at 400% to figure out what was going on, appeared to be almost a pixel to pixel local contrast adjustment. So that piece is ok, although not very convenient to change.
The Save As function needs a Convert to Profile, otherwise have to set ACR to sRGB (I'd rather leave it at ProPhoto), again not convenient to change back and forth.
I believe the interface could be greatly enhanced by creating another control panel tab, say labeled "Output", where various crop and sharpening options, with presets, could reside. It's almost there, I really hope we don't have to wait until 2010 to make ACR really work well as a stand-alone editor, for both screen and print final destination.