I also posted this in reply to another user, but I think it might be useful enough to others that I will post it here so it’s not so buried.

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I’m just starting, after many, many hours, to see the light at the end of the tunnel with Aperture 3. I think A3 offers some great options, and is a diamond in the rough – very, very rough, even in v3.0.1.

But I think I have some VERY USEFUL TIPS for you here (again this is after a lot of learning by pain… 4 different attempts to “upgrade” my A2.1.4 library (42K images about 200GB of images).

1st, and possibly most importantly the “SHIFT” key is your friend. You can use it when you restart A3 to stop the endless processing loop that A3 would fall into every time I upgraded or imported my library to A3 (or 3.01). All you need to do is hold down the “SHIFT” key while restarting A3, this should top all previously stuck processing as you upgrade your library. So use this tip after you first upgrade/import your library, if the processing bug hits. Then you have to be patient and go though your library and figure out where the problem files are (Apple has done a LOUSY job in not identifying what specific images A3 is processing in the “Activity Window” – Let Apple know if this really bugs you)

2nd, at this point you will need to systematically go through your library and figure out where the “problem” files are and “fix” them (in my case all of these worked just fine in 2.1.4 - go figure). I would start by generating thumbnails for all of the images in a project, one project at a time (I had 150 some in my library). When you get stuck in the “processing” loop again, you can restart A3 using the “SHIFT” trick, and maybe just try a chunk of images within that same project until you find where things fail again, and until you can get to the offending image (if it’s a problem you won’t be able to generate a thumbnail for the image – and A3 will go into endless “processing” mode)

3rd, this sound like a horribly tedious process and it is. But I can offer you some useful tips. In my case, and others as well apparently, a lot of the offending files are 16-bit PSD or TIFF images, especially if they had adjustments applied in A2.1.4. In my case I had fewer than 50 of these, so I exported an original and a jpg for each of these files. I re-imported the jpg and deleted the PSD/TIFF from A3 (I kept the exported original for future use). These files would then generate thumbs without endlessly processing. The other type of file that I ran into problems with were stitched panoramic images (often over 30MP) that I had applied adjustments to in A2.1.4. I simply removed the adjustments and the generated thumbs for them (worked like a charm).

4th, download some good podcast, music or audiobook… this will take a long time.

Cheers, and look me up in FaceBook I started a group called “Apple Please Fix Aperture”