I cannot guarantee the uniqueness of the id's or the conformance to standards of the timestamp. Once you set an ID to a feed or feed entry, you must not change it anymore. You must read this article to understand the logic behind an Atom ID.
Your locale settings and your computers clock should be set to the correct time for correct timestamps and ID's.
I cannot be held responsible for any damages due to the use of any information on this page.
Page tested to work with IE, FF, Opera. For generating the id's, my script uses these principles for making a good Atom ID, and I resorted to this page for RFC3339 timestamps. Script does not check for the validity of URL's. Use at your own risk. If you want, you can implement this into your custom feed generator.