@dmaxwell: Had the same problem as you. Logged in minutes ago.
From what i understand you cannot really log in through email id right now, and you seem to have forgotten your username like me.
Just do what i did, open your email mailbox and search "Welcome to gamespot". You'll find the first mail after registrations. In this mail your username is mentioned clearly, log in with that. Hope this helps.
Gamespot really shouldn't make us go through all of this. I mean iv played so many 'prove that you're human tests' since the morning, im not even sure if im a human now.