I've just started using Photoshop (CS6 beta) and having read the Lightroom documentation, it appears that I just choose "edit in Photoshop", do my work there, save and return to Lightroom. Having done this, the image initially appeared as edited, but when I switched to the develop module it reverted to its unedited state, which it maintained after switching back to the library module. I'm not sure what could be causing this behavior, but I wonder whether it has something to do with the layers I created in Photoshop while I was making adjustments. Do I need to flatten them and re-save? Since the adjustments were made in the layers, would flattening and saving constitute be an irreversible action once I quit Photoshop? I realize this not entirely a Lightroom question, but it certainly has to do with the interaction of the two programs, so I hope I've chosen the correct forum for this question.
Update: It appears that this may be a bug. Photoshop created a copy of the original file which sporadically shows up in Lightroom as filename-EDIT. I don't know why it appears sometimes and not others, but this could be an artifact of the fact that it was on my external drive (which is a little slow). I've just moved it to the internal drive, but won't have time to check the behavior until later. Will update then.
Update 2: The problem seems to have disappeared since moving the file to my local hard drive. I suspect that the relatively slow time to save and read new versions of the file on the external drive was the source of the problem.