Hi, I never really bothered to read the back of my pass but it turns out there's a website listed that has the block out dates for 2011 and 2012, located here:
http://www.universalstudioshollywood.com/costco
The next blocked dates for 2011 are: Dec. 26th thru Dec. 31st, and it looks like there are none in January. The one block out date exception which happened to us is, the Costco ticket has to be exchanged at the Universal Studios annual pass processing center which often has a long line. As long as you have not yet exchanged your ticket if the day you visit happens to fall on a blocked date you will be able to enter the park without being charged an additional "block out date" fee, which I think is $20.00.
They will ask to see your ID, if you are with a child they will ask for the full name and birth-date, this info is entered into the system and comes in handy in the event that you loose your pass, $10 fee to replace it. I think it's about $25 to upgrade to an annual pass, and anyone can purchase this Costco ticket, you do not need to be a southern California resident, but you do have to have a Costco membership. Finger print scan required at the turnstile.
Hope this helps!