I wanted to move my (thousands of) images from iPhoto 6 albums into Adobe Bridge folders, but I didn't want to lose my ratings. I never found a way to make the ratings readable in Bridge, but this method turns them into keywords that can be seen in Bridge.
First, turn your iPhoto ratings into keywords. Create a keyword for each rating, and then a Smart Album for each rating. Select all of the images in each Smart Album, and drag them onto the appropriate keyword in the Keyword panel.
Next, convert the iPhoto keywords into embedded IPTC keywords readable by Bridge. Download iPhoto Keyword Utilities, Keyword Assistant for iPhoto, and GraphicConverter, which the iPhoto Keyword Utilities require to run.
Before you run the iPhoto Keyword Utility, launch GraphicConverter and go through the configuration screens. Leave it open.
Highlight the first of your rating Smart Albums in iPhoto and run the "Export iPhoto Keywords to IPTC Keywords" app in the iPhoto Keyword Utilities folder. Repeat for each Smart Album.
Finally, export your images into folders. You can do this last step using the File » Export » File Export command in iPhoto, but you'll have to do each album separately. I used the iPhoto to JAlbum Exporter, which is designed to work with the JAlbum web site, but is a nice all-purpose exporter, too. Note that if you have modified an image in iPhoto, this app exports the modified version, not the original.
To export your images, launch iPhoto to JAlbum Exporter. Select your iPhoto Library folder and an empty folder to export to. Once you select your iPhoto Library, you'll see all of your iPhoto folders and albums. Select and deselect as needed.
Under General Options, deselect everything except for 'Use albumfiles.txt for sorting.' If you don't select this option, the program will append serial numbers to the beginning of each folder and image to maintain the order that you had in iPhoto. Unless you want that, select the option -- you can delete the files later.
Under Export Options, uncheck everything. Under Export Mode, select 'iPhoto Album Hierarchy.' Click on Start Export and go watch TV for a while. Once the export is done, you'll see your iPhoto albums hierarchy (including folders and subfolders) reproduced in the Finder. You'll also see that there are albumfiles.txt and comments.properties file in each folder. Search for each of these two filenames in Spotlight, click on Show All, and drag them all to the trash.
The end result is that all of your images are in folders with the ratings showing up in the Keywords panel in Bridge. If you wanted, you could go folder by folder, filter by each rating in keywords, and apply the appropriate rating. But since you can filter on keywords as well as on ratings, this works fine for me.
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http://hints.macworld.com/article.php?story=20090505042617117