I've just had a quick play with it. The colour rendering is very different to ACR and I would need to do some fine tuning. I think if anything the shadow and highlight recovery is better than ACR, but produces some very strange colour shifts (ACR won't venture into the same realm of highlight recovery). Image structure and grain/noise looks excellent. Viewing is very fast, very clean, but workflow is a bit of a pain with intermediate stages even when opening straight into Photoshop. I do not like the library-based system of importing images, and prefer just to be able to organise my own folders and browse (as with ACR). Aperture still has very nice libraries of images apparently 'there' but of course they are not, they have all been pruned and archived to new HDs etc, but Aperture still shows me them - not something I like!
I would say that if you start from scratch using Aperture, iPhoto, iPod Touch or iPhone for carrying your mobile portfolio (seen this done very effectively by professional David Goff - he showed me his 'book' on his iPhone, which resulted in him getting a feature in Master Photo Digital and a lot of co-operative work since then) - then, it's a really economical, fast workflow and storage management solution for Mac users. But if you have 7,000 existing processed images from maybe 25,000 original archived raws using Lightroom/ACR with .xmp adjustments - as I do - switching to Aperture is not just an easy decision.
Also, the lack of CA correction is a big problem. I use lenses which produce visible CA, such as the CZ 16-80mm on A700 or my current 28-105mm Minolta on A900 (soft, but visible, and best corrected - minus23 red/green for 28mm, plus 20 rg for 105mm, a bit less for lengths like 35mm and 90mm, nothing at all needed from 40 to 85mm). Distortion correction can wait until Photoshop, as it is done with other operations like final cropping, horizon and verticals adjustments, retouching. I have realised that I generally shoot only one master raw for most images on the A900. I don't even bracket. Only very rarely do I shoot multiple raws. Each shot is 'got right' on the spot, as I would expect to do with a rollfilm camera. I then spend 10 minutes per image processing and correcting. Aperture, like Lightroom, will work far better for someone who shoots dozens of shots (weddings, sports, parties, etc) with similar settings and situations.
A typical ACR 5.2/Bridge browser window for me:
http://www.pbase.com/davidkilpatrick/image/107337310
As you may see from the frame numbers, this represents on 27 shots before editing a few (example, one taken at f/10 showing the tiled fountain walk, but repeated at f/22 because I reckoned d-o-f was critical - f10 version deleted during checking). Most pictures are one-off shots, no alternative angles, no bracketing. I generally know what I want and just shoot that one file. A lot of Photoshop work goes into some, for example, the highly distorted picture of the Catalan lady playing an undocumented instrument (it's not a laud, nor mandola, nor a chitarra battente but something related to all of them) - corrected and cropped to restore perspective as if the camera had been flat on to the painting:
The quality from the A900 is exceptional for this type of work as the result is a 48MB file after rescaling. ACR/Bridge/Photoshop is a workflow I find very hard to beat for my way of working. Ref film: I used to work much the same way in terms of setting up the shot - but at the minimum I would use six frames (one filing sheet strip) for each static subject, either bracketing at half-stop intervals with two shots at metered, or 2 frames -2, 2 frames normal, 2 frames +2. For commercial shots we used to shoot one entire 36 exp roll of E6 per shot - six identical frames -1, six -0.5, six 0, six +0.5, six +1, plus another six at a further half stop bracket in whichever direction seemed most useful. We would also use one entire 120 roll of E6, three bracketed frames of C41, three bracketed frames of b/w 120 (Hasselblad backs made this easy); and then five sheets E6 5 x 4, three sheets C41 5 x 4 (we never shot any b/w 5 x 4).
Today - one raw file...
David