I worked with WordPress as a web designer for years, and this is the first truly professional, intuitive and flexible solution for a whole myriad of every-day needs I found (and I tried pretty much all).
In addition to being an excellent form maker, Formidable is an amazing front-end solution. I can finally set up usable front-end entry/edit pages fast and easily. Templates for entry displays are easily created and assigned, and there's a great shortcode interface, including conditionals. Adding the ability to work with native WP fields was a stroke of genius, as well as the ability to assign a Formidable custom field to standard WP meta data, making it ultimately usable with other WP features & plugin. This is my must-have plugin.
Support has been stellar, as well.