If I had to pick one of those, it would be reducing work. People will pay for something that makes their job easier / efficient. Knowing what people want is hard though. I personally attribute it to day after day of paying attention to the details in support, design and all other areas of a business, which slowly builds trust and paying users.

Of the three, my guess would be making web-form creation accessible to people who could not do it before. While it's great to save time, that's a percentage improvement; whereas making the impossible possible is of a different order altogether. It's also to get people to adopt if they haven't already invested in a way of doing it that is already working for them (even if it is inefficient etc) - change is hard when you have bigger problems to worry about. But that's just my guess - I'd love to hear from the wufoo team...

But I agree with you about the support, design etc. There are a few companies providing online forms. Technically, it's not that hard to do; and I had a quick play with a competitor, that seemed pretty good. So I guess the "what people want" above just defines the mini "industry" of online forms - if Wufoo's is within an industry, its success must be based on additional factors, like the ones you mention.

"I'd love to hear from the wufoo team..."

That would be me :) I'm one of the co-founders.

whoops! Sorry, I am chagrined :/ But, bonus, I got an answer from a co-founder. Thanks!

I thought you were speaking hypothetically (I checked your profile too).