Not everyone is going to shell out $500 for Aperture when it arrives. So Apple needs to keep iPhoto in good working condition. They took a step in that direction with the latest system update, 10.4.3.
Prior to the update, I wasn’t able to load my .CR2 Raw files from Canon’s Rebel XT and 5D into iPhoto. This really busted up my Raw workflow and forced me to use Canon’s Digital Photo Professional for browsing my Raw thumbnails. Adobe Bridge is just a tad too slow at initial rendering for my tastes, although I really like Camera Raw for image editing.
Mac OS X 10.4.3 fixed all that. So, for the time being, I can go back to iPhoto 5 for organizing my Raw files.
As a side-note for you iPhoto users who are considering upgrading to Aperture, there’s an import function in Aperture that enables you to grab the images from iPhoto and put them in the new environment. This will make the transition much easier.