Last night I tried the new public "Start Playing" because I've really been wanting to see the new tutorial and start area. (Nicely done!) A looooong time ago I made a second Glitch account. There was some confusion on policy about alt characters and as a result I deleted that account, using the red "Delete my account" link on the account page. The character shows as deleted. http://www.glitch.com/profiles/PUVCE3R3K7I2SCU/
When I got to the point in the tutorial where you have to register, I entered the email address I had used for the old deleted account. The game client informed me that there was already an account with that email. Confused, I went to Glitch.com and tried to sign in to see if the deleted account was still active. I got "Nope, we don't have an account with that email address."
So... My email is both associated with an account AND not associated with an account.