I gave a class last spring and saw one of the attendees the other day. He said "ya gotta clear something up for me". In the class I had taken an image from Adobe Photoshop Lightroom 3 (after going as far as I could initially) over to Adobe Photoshop CS5. There I played with adding a couple Layers, added a couple pieces from other images and generally messed with the shot. When I was done there, I wanted to do other things back in LR3. The part the fellow wanted clarification on was how I saved it. That took me back a little and I asked "what do you mean"? He explained that he "always" does a Save As rather than just plain Save. I asked him to tell me why he did that. That's when I saw why he wanted some explanation. His justification for using Save As was that he wanted to preserve his original image. Take a look at today's image. It's the same shot, four different ways. The original is on the upper left. The other three have had one, two and three trips over to PS CS5 and back. Each time, a simple Save was used, yet there are now four files that show up in LR3. (It also applies to Adobe Bridge.) To find out what's going on, hit the "Read More".
First, take a look at the image in the upper Left. It's TJP5120.NEF. It's a RAW file. The one big thing about a RAW file is that you CANNOT do anything to it that changes pixels. You can do all sorts of tweaking in LR3, but it's all nondestructive. The entire list of the changes made to an image is kept in a file that details every step that was made. It stays with the image and can be accessed today, tomorrow, next week, or next year. The "original" image doesn't change. You can always go back to it at some time in the future.
Okay. The image is tweaked in LR3 and brought into PS CS5. Things are done to the file, adding Layers, moving pixels, cloning things in or out, anything. The only reason to bring an image into CS5 is because you want to do something physical to it. Once that's done, many people want to use Save As because they want to make sure not to overwrite the file. Couple points. A simple Save will make a new file, not overwrite the old one. The "old one" is a NEF file (in my case, a Nikon RAW file) and NOTHING can be done to a RAW file. A physical file is created in the directory folder that the original came out of. With today's image it becomes the TJP5120.NEF-EDIT.psd seen on the upper right. Using the straight Save command it not only saves the files, it also adds it to the LR3 catalog and it shows up to the right of the original. If Save As is used, the "adding to the catalog" doesn't happen. You would have to Import the file into LR3 using the Add option. Plus, the Save As will save the file in whatever folder was last opened, not necessarily the folder containing the original image. Therefore, it is possible to have the files scattered all over your computer. Not a good thing.
In the lower left you can see a version of the image that took a quick trip to CS5, had a Topaz Adjust preset thrown on it and a File/Save done. Because there was "nothing" done to the image in CS5 (it was done in a plug-in) saving it to LR3 understands that it's not the same as when it went over to CS5. It now saves the new version of the image as TJP5120.NEF-EDIT-2.psd. Anything that you'd want to do in LR3 can now be done to that file. Let's send it over to CS5 one more time.
The result is the image in the lower right of today's image. A couple Adjustment Layers were added to the image, the base Layer copied and a Smart Filter run on it. "Things" were done. Using the Save (File/Save) function puts and file in the correct folder, Adds it to the LR3 catalog and shows it to the right of the version used to bring it over to PS CS5. Now it's named TJP5120.NEF-EDIT-2-Edit.psd.
There appears to be a limit of three "EDITs" available in LR3. I've actually gone further than that, but the most I've ever seen has been EDIT-EDIT-EDIT. If you're not finished screwing around with your image by that point you're doing more to your image than I've ever done to mine. Hope this "explanation" helps get you to use the Save function to bring your CS5 image back into LR3.