My current workflow is a bit different to the OP:
- I use LR to do all the image-based adjustments, selects and exports
- I shoot in RAW (Nikon NEF)
- I use PM for all captioning
So:
1. Import RAW images into LR3
2. Select the images I want to caption (I use stars as my rating)
3. Save metadata to file (this makes LR3 make a XMP sidecar file)
4. Open the folder in PM and select the files that have 1 star and higher (or whatever tagging you use). Don't worry if your image edits don't show up in PM as your prefs may be looking at the embedded jpeg file and not the RAW
5. Caption away. Note that the captions are written into the XMP file AND the RAW file if that's how you've got it set up.
6. Be careful not to change the rating of the images in PM as there are problems with LR reading those changes back from the sidecar file. Just doing IPTC changes in PM is fine. (see discussion
http://forums.camerabits.com/index.php?topic=5428.0;topicseen)
7. When you have finished captioning switch back to LR3
8. Select all the files that you've captioned and select Read Metadata from Files
9. Export the images as you need