According to Apple, the Aperture 2.1.1 version “supports various general compatibility issues, improves overall stability, and resolves a number of minor issues.” Unfortunately, the specific changes made in the update have not been published.
When Aperture was updated earlier this year, it incorporated an open plug-in architecture that allows any photographer to use third-party software in Aperture. Aperture includes the plug-in developed by Apple Dodge & Burn, by which brush-based tools are added to lighten, darken, adjust contrast, saturation and blur images. Currently, there are several companies that have developed and published plug-ins for Aperture.
The 48MB update can be downloaded from the Apple website.