Designing web forms can be tough all by itself. There is a lot of markup to get right to make sure it's accessible and has good UX. There is a lot of CSS (properties you may not use every day) to wrestle control and make sure things look good.
Wufoo's got you covered there. It's almost trivially easy to build forms (even quite complex ones), and good design, good UX, and good accessibility come along for the ride.
But what happens after you submit a form? That's just as complicated as the HTML and CSS. There is validation, spam protection, and processing, to name a few. If you're really doing it right, you'd save the form data to a database before sending it along elsewhere (like to an email notification or integration). That way you always have the data in case anything goes wrong, or to look at in aggregate. Of course, you get that with Wufoo too, with full blown API access to all the data.