This is one of those times. While there have been some discussions about potential changes to the form, they are not in place just yet and so the current form will need to be used beyond its current expiration date of August 31, 2012. So, if you knew there was expiration date - and even if you didn't! - you can continue to use the current form until further guidance is provided.
Employers would be wise to check back in with some regularity at the USCIS website - www.uscis.gov - to determine whether a new form or a form with a revised expiration date has been issued; HR Matters will also provide updates through our blog so check back!