I've been using Alphanumeric order increment id's since ~CE 1.1 - they're all set up using an alpha character in the prefix field of
At the time there was no real documentation surrounding setup and multi-store setup, so we adopted the practice that all order id's were prefixed with an Alpha that represented the store. Order numbers typically looked like M000000003, PA000000004, etc.
Fast-forward 5 years to EE 1.11 and since approximately PE/EE 1.10 we have noticed that orders periodically return a
SQLSTATE: Integrity constraint violation: 1062 Duplicate entry 'PA00505156' for key 'UNQ_SALES_FLAT_ORDER_INCREMENT_ID' error or something similar. It's infrequent - but my research leads me to the fact that a race-condition while reserving the order ID might be due to the prefix being alpha and not numeric.
I know that Ashley Schroder was working on this a while back, with a Pro edition of a module he developed - http://www.aschroder.com/2010/07/easily-set-a-custom-order-number-in-magento-with-my-free-setstartordernumber-extension/ - But it doesn't look like there has been much movement there, as the pro version isn't on Magento Connect.
Is anyone else using alpha prefixes? How has it performed for you so far? Do you see the same errors?