You are overlooking a very strong alternative: Bibble/Bibble Pro.
See
http://www.bibblelabs.com .
I bought Aperture a couple of months ago (before 2.0, admittedly) and consider it to have been a complete waste of money. Although I spent many hours with the training DVD, reading documentation, and practicing, I just cannot get my work done with Aperture as well nor as efficiently as with Bibble Pro.
Literally, after all the above, I spent 2 hours trying to do what should have been a straightforward post-processing of a single shot. With Bibble, my throughput would typically be fully 100 to 200 shots per hour (except for the occasional frame that needs major surgery).
Cost: 129.95 for the pro version
Trial period: 14 Days
Multi-platform: Linux, MacIntosh PPC, MacIntosh Intel, M$ windows
Multi-threaded: see the web site for explanation
I especially like that I can spread the load out over multiple machines. For example, I can do manual edits on my Mac with small batch processing going on in the background, while simultaneously running a huge job on my Linux server creating multiple-size versions of images and storing them directly on my web server. Or I can do the preceding vice versa, etc.
Aperture gets the prize for the slickest interface, but the Bibble interface is "greased lightening" by comparison. Which do you think matters to your clients? Aperture also brought my dual 2.7-GHz PPC to a crawl while Bibble cruised right along.
Bibble also comes with Noise Ninja, a brilliantly executed straightening tool, and all the other things you expect. (Full Ninja functionality costs a little extra. You may not need it, though.)
--
Thomas D. Shepard, Sc.D.