iPhoto 6 adds some terrific options to Apple's digital shoebox application, including better handling of Raw files, ColorSync management, and a non-managed library choice. Today I want to give you a brief overview of how Raw file editing has evolved in this latest release.
First, let me describe how Raw file management worked before in iPhoto 5. If you had Photoshop selected as your external editor, double-clicking on a thumbnail from a Raw file in iPhoto 5 would open a Jpeg interpretation of that Raw file in Photoshop. You could edit this Jpeg and send it back to iPhoto by saving in Photoshop. If you wanted to work in Camera Raw, you had to drag a thumbnail from iPhoto 5 on to the Photoshop CS icon on your Dock (this worked only if you haven't edited the file previously in iPhoto 5) or export it as "Original" and open that file in Camera Raw.
After editing in Camera Raw, you would click the open button to move the image to Photoshop where you could save it in any format you wished, or just hit save and choose your format there. You could then add the edited and saved PSD, Tiff, or Jpeg back to your iPhoto 5 library as a new image.
In iPhoto 6, you now have the Use Raw files with external editor option in the Advanced Preferences pane (iPhoto > Preferences > Advanced). Using this option changes your workflow considerably.
When the "external editor" box is checked, your double-click on a Raw thumbnail opens that image in Camera Raw (if you have Photoshop CS selected as your external image editor). Now, as far as I can tell, you can't "roundtrip" the changes back to iPhoto 6 just by hitting the "Done" button. But you can save to another format and import the edited Tiff, PSD, etc. back into iPhoto 6. So even though it doesn't technically "round trip" your Raw edits, this new method does save you a step... and is a welcomed improvement.
What's interesting though, is that iPhoto does remember your Raw adjustments made in Camera Raw. If you double-click the thumbnail again, it opens it in Camera Raw with your previous settings in place. [Update from a reader: it's actually Camera Raw that remembers your settings. Thanks Rafa]
If you want to edit your Raw file in iPhoto using the Adjust palette, you can go back and change the preference. But I prefer to leave the preference setting as it is and simply Option double-click to switch to iPhoto's editor, or CTRL-click on the thumbnail and choose either "Edit in a separate window" or "Edit using full screen." In my testing, I seemed to be working with the original Raw data using these options, opposed to building upon any instructions I've added using Camera Raw.
Now, if I uncheck the Use Raw files with external editor option, iPhoto 6 behaves just as it did in iPhoto 5 -- I'm working with a Jpeg interpretation of the Raw file, and my changes are saved back to iPhoto 6.
There's more to discover here, but I hope this gives you a good start with the editing options for your Raw files. If you would like my overall initial take on this application, take a look at iPhoto 6 First Impressions.