They seem to now be requiring you to spend X amount of real money before you can redeem X amount of voucher credits. For example Spend $25, get $100 advertising credit. With terms like, To qualify for the promotional credit you must accrue advertising charges in the amount of $25 within 31 days of entering your promotional code, and other terms like, Your account must be successfully billed by AdWords and remain in good standing in order to qualify for a promotional credit. The promotional credit will be applied within approximately 5 days of your account reaching the threshold for accrued advertising charges specified above, as long as you've activated your account using the promotional code and fulfilled all requirements stated in the offer.
My guess, that part "...and remain in good standing in order to qualify..." means, you get just ONE violation, bye bye voucher. The source where I was getting mine has been doing this since the beginning of august. I think this is the end of all voucher methods.