I've read through the PS blog and the moderators seem to contradict each other. One guy says the money needs to be spent by "sometime" in december and the other guy says that the code just needs to be redeemed by Dec. 9th. Any ideas?
I would defer to the email sent with the $20 code, and this is a direct quote;
"Code expires Dec 9, 2012. Once Code is redeemed, however, the $20.00 Sony Entertainment Network Wallet Top Up can be used even after Code expiration."
So I think that clearly states that the money won't be removed from your wallet once there.
On a side note, that mod doesn't sound very knowledgable. It's a balance - you can't track specific dollars. I added a bunch of PSN cards, and had about $30 sitting in the account. This added to that.
Since I can't specify which dollars I want to spend, so if the $20 rebate expires, that would mean I would have to drain the entire account in order to ensure I had spent it. Just doesn't make sense.
If they wanted the credit to expire, they would have made it so that you used the code to make the purchases until the total amount was used, or expired.