I am also having issues with the gem store. I have bought gems once successfully. After trying to buy more gems the day after (8/26/2012), it just keeps failing at the final approval stage. I’ve tried my debit card, my wife’s credit cards, and my PayPal. I keep trying every day and it has not worked since my first purchase.
My ticket number is [Incident: 120831-009921] and it was submitted on 8/31/2012 with no response at the time of writing this post.
Edit: I should mention that similar problems have been happening to me before with Aion for years, and even with buying the digital download of Guild Wars 2 itself. Mostly it was solved with some sort of 24-hour white-listing on NCSoft’s end, although it would be nice to have a permanent solution.