And, yes it appears that this problem only affects PCs. For you Mac people, I have one question: when you installed B4, did you get a dialog box stating that a "one time" database conversion needed to be made? PC people did, and I'm wondering if this could be part of the problem?
My upgrade process on a non productive environment Powerbook:
1. Backup library and pictures.
2. Install Upgrade
3. Database conversion. The same dialog box as when upgrading from Beta 2.0 to 3.0.
4. Rendered the previews
5. Left the powerbook for a couple of hours to finish the render
All 'seems' quite stable. If things continue liek this I will try it on a productive machine and database over the weekend.
So far so good. That said I will also have another look at Aperture as some of the 1.5 updates should make it a much more useable program for me. The loupe in the current version of Aperture is better than the Lightroom approach. More imortantly it also shows a high commitment from Apple to the product.
Off topic. I think we are very lucky to have 2 established and innovative companies working with such intensity to meet many of our needs.