after several days of using it, i'm very, very happy. it's much faster, has presets similar to LR, and fixed a lot of annoyances that we learned to live with in A2. once people figured out to import library and turn off faces during the import, and then reprocess on a library-by-library basis, none of the slowness problems occur (most all people that had slow system issues with the upgrade had not waited until it finished processing the imported images). my main library (700gb) converted in about 5 hours. my sports library (about 190,000 (mostly) .jpg images) converted in about 40 minutes.
working with a 5dmk2 raw file was smooth, even with adding a lot of adjustments, rotation, cropping, and some applied presets. i feel the loupe is far less laggy that A2. i do miss the previous eyedropper but i'm sure i'll get used to the new methods.
this is running on my macpro in 64bit w/ 8 GB ram and GeForce 8800 GT. i have noticed it's fairly slow on my MBA (2 GB, 128 GB SSD , GeForce 9400 M).