Apple has just released an update to Aperture 3. You can access the update via Software Update in your System Preferences or as a standalone file from here.
From the release notes:
This update improves overall stability and addresses a number of issues in Aperture 3, including:
- Upgrading libraries from earlier versions of Aperture
- Importing libraries from iPhoto
- Importing photos directly from a camera
- Memory usage when processing heavily-retouched photos
- Face recognition processing
- Adding undetected faces using the Add Missing Face button
- Printing pages containing multiple images
- Printing photos and contact sheets with borders and metadata
- Editing photos using an external editor
- Display of images with Definition and Straighten adjustments applied
- Zooming photos in the Viewer and in the Loupe using keyboard shortcuts
- Accessing Aperture libraries on a network volume
- Selecting and moving pins on the Places map
- Adding and editing custom locations using the Manage My Places window
- Switching between masters when working with RAW+JPEG pairs