Apple just released a 2.1 update to Aperture that adds various refinements and takes another step towards opening the application to software developers.
The most prominent addition is a Dodge & Burn plug-in, which demonstrates the new plug-in architecture. You can
watch a video about this feature here.
What we learn from this is how Apple has elected to approach image editing plug-ins: they have punted on opening up the metadata-based image pipeline and simply grafted on a pixel-editing-based system to Aperture. If you want to use plug-ins to modify your imagery, Aperture cooks a TIF file, stacks it with the RAW original, and then opens a special editing window. Instead of shelling out to Photoshop, you stay in Aperture, but the fundamental process is the same. Whatever changes you make to your image in the plug-in are permanent (destructive) and once you leave the plug-in, you can go back, but only to pile on more changes.
On the one hand, this approach is practical, because it will make it straightforward for a gazillion Photoshop plug-ins to be ported to Aperture. Lots of new capabilities could be quickly added to Aperture by third parties, further reducing Aperture users' dependency on Photoshop.
On the other hand, this approach is bitterly disappointing.
Yet another pixel editing framework couldn't be more retrograde or against the spirit of Aperture. Moreover, the implementation—at least based on my first impressions—is a shockingly inelegant user experience. It feels like a hack.
You can update to Aperture 2.1 through the
Software Update... feature of OS X.