The calculations do not involve modifiers like demon hunters sharp shooter, however, there is a skill bonus % field where you can input this information.
The basic calculator gives a quick way to check damage and compare new weapons.
The advanced calculator is a bit more complex and involves entering all items individually.
The about/contact page is still a work in progress, as I've been doing this during any free time at work. It has gone down intermittently but appears to have stabilized enough for me to release it to the public (that's what happens when you have a crappy host / domain registrar =P)
I am currently working to convert this to PHP so we can eventually link item builds around the community.
** UPDATE ** You are now able to save advanced builds by getting a URL link. After you are done, just hit get link at the bottom and a link will be generated at the top!
You can save this link for your own records or post to other forums! Here is a sample URL: http://tinyurl.com/7yorlp5