Does Simple allow for sending checks from an online interface yet? If they don't, that's one point for GoBank.
It does look like GoBank is doing instant person-to-person transfers, which Simple doesn't have just yet (but they've said is coming soon).
Speaking of, it would actually be pretty cool if I could send money with Dwolla directly from Simple :) Dwolla's iPhone app is terrible, and their web interface isn't much better.