I've used Wufoo on a few sites, quite easy
I think another unsung advantage of woofoo is that they ALSO build an accompanying database for the form.
Remember there are 5 parts to a form.
1) The HTML markup.(the actual semantics and elements)
2) The CSS styling ( the look)
3) The behavior (usually done in .js) (the focus on elements, do fields change when other fields are selected? pop up windows for extra inputs..ect)
4) The DB ( where does this data go?)
5) The process ( what does the data do) for example in a log in form if the "passkey" field doesnt match a predetermine string.. go back t the form, else go to a specific URL.
Your question might be more easily understood broken down as outlined above.