Thanks for the replies.
On balance, while I like LR 4 and its interface, that blue hyperlink at the bottom of the ACR screen is its killer application, IMHO, and the reason I'll probably continue using ACR most of the time.
I want to be able to switch between colour spaces in a more orthodox way - soft proofing just doesn't feel right.
Also, if I use ACR, I@ve got 0-255 across the board. Oscillating between 0-255 and % in LR is silly, and you really have to wonder why they allow it.
I also miss the colour sampler tool, which I use a lot.
This just keeps ringing in my head... "Adobe apparently intends to make Lightroom
easy for the user by limiting the options." Andrew Rodney.
LR should be an exact copy of ACR with bells on, and it isn't. ACR was perfected over many years and some of its best bits were omitted in LR - they shouldn't have been.
Ps. ACR ain't perfect either. Some things LR does better, e.g. the Spot Removal Tool. In LR, after clicking on an area, you can hover over the next spot and resize for it BEFORE clicking on it. In ACR, if you try to resize before clicking, you enlarge/make smaller the previous spot instead. So, the LR way is more intuitive, in my view.