In the past I have done very little in LR other than temp, clarity, and maybe vibrance before going into photoshop. One feature in photoshop that I like to use is selective color. Is luminance in LR 4 the same? Why is there no gray slider like there is in photoshop?
As already noted, luminance in LR is not selective colour; in LR, use the HSL panel (hue, saturation, luminance).
There is no gray slider in LR (probably) because it is a very different program. LR never edits your original JPEG/RAW files.
If you totally muck up an image, hit RESET in LR, and your original is back with no changes at all.
The internal workings of the programs are very different, so I find it interesting that CS and LR have very similar controls.