The 125MB update is recommended for all users and according to Apple, the revision "addresses more than 100 issues related to overall reliability and performance in all areas of the application."  More specifically, Aperture 1.5.1 address issues in the following key areas:

• Keywords
• Loupe
• Cropping
• Previews
• Metadata presets
• File renaming
• iPhoto Library import
• Watermarks
• Consolidate/Relocate
• Managing Referenced Files
• Lift & Stamp
• Print dialog
• Image Deletion
• Miscellaneous issues
  

Additionally, at the Photo Plus Expo in New York, Apple announced that customers can participate in a free fully-functional 30-day Aperture trial. Customers can download and install a fully-functional version of Aperture 1.5.  The trial includes all the features available in a licensed copy, but the trial version lacks the sample images and tutorials that ship with a purchased version.  Note however those items can be acquired if customers decide to place an order following the conclusion of the 30 day trial period.

With Aperture, users can import JPEG images from the majority of today's digital cameras. Aperture also supports the RAW format from a wide range of digital SLRs.  You can even work with TIFF and PSD images.

Please visit the Aperture Technical Specifications page for a detailed description of Minimum System Requirements.