I have found the absolute gold standard for sign up forms at Spreadshirt:
That’s it. One field. No fiddling with duplicate passwords, no CAPTCHAs, nothing. Enter email, and you’re ready to accomplish tasks. In this case, design stuff (like t-shirts) to be made on demand:
One click from “sure, I’ll try that” to getting to the meat of the service. It’s perfect. Why don’t more services do this? OK, I know why. But this is absolutely one place where taking the time to answer the question “What do we have to have from users to get started?”— and not being willing to take shit from developers who don’t want to go the extra mile to overcome technical limitations— can turn a routine, tedious experience into an EPIC WIN.