Today Aperture has released Aperture 2.1 for Mac, very soon considered that version 2 was released just a month and a half ago.
The update includes some bug fixes and feature tweaks but, more importantly, it introduces a new expansion possibility with a plugin framework (on the same way of Photoshop for example).
Already some known plugin developers like PictureCode (producers of "NoiseNinja" for noise removal) are working for an Aperture version of their program.
Apple includes a burn and a dodge plug-in but it will be interesting to follow this evolution with thirdy party producers.