Weird. David, I'm having the exact opposite issue - images are DARKER when I edit in Photoshop. It's like only some of the toning that I do in LR actually makes it over to Photoshop. I'm also getting a warning about compatibility with ACR 6.7, but when I check "Updates" in Photoshop I get assured that everything is up to date. Frustrating.
On my machine anyway, when I go to Photoshop (CS5) Updates, it says everything is up to date even though I know there is a new version of ACR or whatever out there. And this is for several weeks after the new update. So I have to physically go to the Adobe Download Center and download the new update.
Several of the External Editors are now Exporting the files out of LR in the sRGB Color Space even though your original intentions are ProPhoto. Then after you change everything back in preferences to PP, it reverts back to sRGB unless you redo the drop-down menu to "Save Updated Preset".