Wufoo do most things well, including the signup process.
Interesting form. I hit tab to go the the submit and it actually scrolled me over in a suboptimal way.
I suspect that's specific to your browser, whatever it is, as I'm not seeing it in Firefox or Arora (WebKit+GTK browser). I imagine they'd fix it if they knew the specifics of how to reproduce it. They sometimes show up around here.
Checkout github; from any non-payed account they make changing to a payed account easy. Definitely worth looking at.