I try to do some basic RAW processing before I combine into a panorama, because there are some things which are harder or impossible to do after conversion.
For example, suppose there's a patch of sky or something with the highlights slightly blown. Once it's converted to TIFF/JPEG there's nothing that can be done, but in RAW it's an easy fix. So I tweak it in RAW and then use Lightroom to sync my change to the other images in the sequence.
Same thing with white balance: tweak in one image if necessary and then sync across to the others. It's easy enough to flick between one image and another, so if a change looks right on one image but not quite right on another then I can undo or re-tweak.
I also use this approach for things like contrast, vibrance, saturation etc. but a little more cautiously because they can be done after conversion to TIFF/JPEG.
I haven't yet got my head round sharpening. I can't work out whether the stitching/blending software would cope better with sharpened or unsharpened images. My instinct says stitching will be better if sharp, but blending will be better if not sharp ... so I tend to leave sharpening until the end of the workflow, just as with normal images.
