And as expected, Mr. Gruber downplays this terrible, terrible bug. http://daringfireball.net/linked/2010/10/25/castro-iphone

If Microsoft released an update to the software which wiped out data as precious as your personal photos, there will be much more uproar.

Wow, unbelievable. Gruber appears to be nothing more than an Apple mouthpiece now.

That's one nasty, nasty problem.

But why would iPhoto keep the photos themselves in any other format than the original files and just point to them from the metadata store? The most I would to with the files would be to compress them using some lossless (obviously) algorithm... This way, the worst that could happen would be metadata corruption.

I'm pretty sure iPhoto does store them in their original form—unless they were originally in RAW, in which case they get converted to .jpeg, I think.

Then why would there be a risk of data loss during a version upgrade?

I'm not sure. I'm just commenting that in iPhoto (and I just upgraded to '11) they are stored uncompressed and in their original format.