Eek! I just registered and have been waiting for my account to be approved to post this:
Even though the sales aren't live yet, if you're waiting for the Big Bang Theory: Season 4 set, there is another SKU that has gone on sale--and the Blu Ray is actually cheaper than the DVD set!
Search these SKUs--
DVD: 3158389 ($18.99)
Blu: 3158167 ($8.99)
Good luck!