The sign in with twitter was more prominent but we actively took attention away from it so that people would see the sign up with an email address first. By enabling sign in with Twitter, we lose a communication channel that we could be using.

Would you say that losing a user's email address is worth it to make the chances they'll sign up higher?

You can let them signup with their twitter account, but then prompt them for their email address. Almost like a 2 stage signup. Best of both worlds. Click a button to sign in with twitter, enter your email address and get started.

If you expand to facebook let me know. I would love to filter out the spam from my family members about MLM crap. :D

We did actually consider prompting for an email address once they sign up with Twitter. However, whenever I've used an app that does that to me I just leave the site and don't go back and thought that if I didn't like it happening to me, it wouldn't be fair to do it to others.