How could implementing OpenID and OAuth for Twitter be faster to implement than a User table? Certainly you've built web apps before, and therefore have a login workflow that you can rip out and drop into a new site in the first 5 minutes of development?
One other thing you're missing is that as a new user of your thing, I don't trust you enough to hand across my twitter username or openID. I'm more than happy to create a throwaway account with you, but you're certainly not going to get any information that links my profile with you with my profiles elsewhere.
In short, you're losing a significant fraction of your potential userbase. Right now, since this is the moment when you've got more exposure than you'll ever have again. Spend 20 minutes getting a user/pass thing implemented right now, before the sun comes up in the US, and you'll quadruple your first-day signups.