Kinda sucks for me, as I've almost exclusively used gift cards for the last few years. I get a bonus tax-free credit card by my employer, which I can only use at retail stores. So those were a great way for me to use that card to buy games. It was also a good option for people who wanted to avoid payment providers like Visa/Mastercard etc. Oh well.
This is a huge blow to me. I'm not sure what to do now, because the Steam Gift cards was a major reason to use Steam for me.
Technically pre-paid debit cards will serve the same purpose if you still want to use cash to buy a card to redeem steam cash with. You could also use something like PayPal if you don't want to expose your card directly.
I got steam gift cards as presents growing up, so I feel ya though.