How does Amazon deal with Metadata ?

Hi GIBBS,
Each Amazon S3 object has a set of key-value pairs with which it (metadata) is associated. There are two kinds of metadata: System Metadata and User Metadata.

System Metadata is used and sometimes processed by Amazon S3. It depends on API (REST or SOAP) being used.
User Metadata has nothing to do with Amazon’s functionality. It is simply a piece of information that creator of file includes to make it clear as far as understanding is concerned.

Meta data added by user can be of any length but must conform to US-ASCII when using REST and UTF-8 when using SOAP or browser-based uploads through POST.For both REST and SOAP requests to Amazon S3, user metadata size is limited to 2k bytes for the total length of all values and keys.

Please visit following page for more details:
http://www.bucketexplorer.com/documentation/amazon-s3--upload-object-custom-header-or-metadata.html