I haven't finished my site, but the awesome power of this plugin can be seen from this law firm's online conveyancing quote pages.
The form places all the HTML in the right place, calculates all of the different options (some quite complicated nested IF formulae there...) and then provides the total quote.
The email gives a fully itemised quote with all of the different variables and a whole lot of other custom text.
So it really is a great plugin.
Just need to add a few things to make it perfect:
a) Ability to clone forms so that they don't have to be recreated from scratch;
b) Captcha and or Akismet to block spam
c) HTML in the emails it can send so that a full corporate image can be created
d) Conditional showing of dialogue boxes so that questions can be asked when necessary but not otherwise.
It'd be nice to hear from Igor about how plans for this are going.