After making every user worry about it's commitment to the program, Apple finally released Aperture 2.0. Quite desperate for improvements, I immediately downloaded the demo, then purchased a serial number and after a few days of playing around, migrated my 100,000 pictures library to it. It's not bad at all.
1) the weirdest change is how the interface has been streamlined to the point it gets completely out of your way. It makes the software look much less powerful when in fact it is probably twice better than version 1.5. As a result, you can spend your whole time in the full screen mode having your picture, as it should, taking centerstage.
2) it is seriously faster. Maybe not as fast as the competition leaders, but certainly fast enough so it isn't really an issue, even on older hardware. Of course, you have to be reasonable and wait until all background tasks have been done (or paused them, you can...) if you want the best responsiveness.
3) the image quality of the RAW converter has been seriously improved, the reason why it took so long to provide support for new cameras.
4) a few welcome enhancements have been added, some pinched shamelessly from Lightroom, like Vibrancy and Recovery sliders.
5) Apple showed it is interested in the product and improving it. Plus, it is cheaper than it was so maybe it will make Lightroom cheaper as well: everybody is happy.