Good question. I just signed up from a page that stated I would get $50 in my account- but have not seen it in my account anywhere- and no place to add it in. Sent an email to support- then sent a second with the $75 code above. If these don't work out, I'll be asking them to delete my account and I'll stick with Adwords and MSN. I get tired of chasing these programs down for something as simple as a promo code.
I tried looking for their e-mail address, and I couldn't find it. So I just called them, and they entered the credit manually for me.
Ya, for new signups only. I'm not sure where you enter the code since I'm already a customer. It should work if you call though.