Same issue did you find a solution?
I basically left it - and left it - and left it. Eventually it recovered, and started importing photos. So my experience was that it will work eventually - it just takes ages, and looks like it's hanging at first.
I think I left it for three days in total. After the spinning beach ball appearing for many hours, it did start slowly importing.
That's crazy my library is 300GB so not sure it will ever complete. Has to be an easier way...thanks for the reply
One thing the importer does is copy your photos out of a managed iPhoto Library, if you use that option. If you had referenced photos, it probably would go quicker, although I haven't tried it. And you could also try the other importer that is in the Mac App Store (I think there may be a demo on the developer's web site, or do it manually. Sort of depends on what you need to keep from the info you're put into iPhoto.