Dwolla has stated up front from when I first heard about them that ACH chargebacks were possible.
... and yet all their marketing stuff says the opposite. Landing them firmly in the bullshit, "as seen on TV" category.
I don't have a problem with chargebacks, or anything Dwolla has done. I actually like the service, and I still use it (sparingly). But you have to call bullshit when you see it.