I can confirmed, as of Jan 9th, 2013, Gift2go cards still DO works for Signup with paypal.
But not for lifting paypal limit.
I've cards with 4/20 and 8/21 exp date. Both work for PP signup. However, I've tried the 4/20 card to lift pp limit but was unsuccessful. I've not trie the 8/21 yet so not sure if it will work or not.