Not sure if it is released to coincide with Adobe Lightroom’s major upgrade announcement, but Aperture 2.1.1 update is now available. It is a x.x.1 point update which normally means a bug fix release. The description from Apple:
The Aperture 2.1.1 update addresses general compatibility issues, improves overall stability, and resolves a number of other minor issues. The update is recommended for all customers using Aperture 2.
Important Note: Aperture updates available via Software Update or the Aperture Download page can be used only to update full versions of Aperture. They cannot be used to update Aperture Trial software, currently Aperture 2.1.
The update is available via Software Update or Aperture 2.1.1 download site, which require you to sign in with your Apple ID for the download.