Guys remember that people come here to look for solutions to problems so what you are seeing is weighted towards negative experience.
I am running what would be considered a high spec machine, 10.5.8 and 2.1.4, I have 70k + images in my managed production library, 80% Canon RAW, remainder jpegs, images are stored on an external 1.5TB RAID, the Mac is a 2x 3GHz Quad Core, 5GB RAM, dual monitors off an ATY RadeonX1900.
Very occasionally I may get slow performance, but given I am working with a 21MP file from the 5D MKII, I accept that. Usually I am doing something stupid like stamping 100+ images with a half dozen adjustments. I think if I was trying to do this on a lesser machine I would be very frustrated, but if that is the case I should accept that I am asking quite a lot from my machine.
I have not upgraded my OS as this is a production machine and until I know for certain that all bugs are ironed out I will continue with a working system, I can not afford to have my production machine being used as a test bed.
I know that many of you who are having problems do not need to hear this now, but unless you are the sort who is prepared to do trouble shooting, read the manuals, do clean installs etc, next time hesitate and watch these forums to see what people are experiencing prior to doing an upgrade.
In the meantime ensure that you who are "testing" the new OS AP combination for me report your issues to Apple via the feedback pages.
http://www.apple.com/feedback/
My experience with Aperture from the start has been very positive and sorry but many of the issues arise from not reading the manual, be it the AP, OS, or other device/software installed on the system.
Tony
(Rant finished, ducks his head expecting to cop flack over this one).