Have you ever wanted to send a user to a form to fill something out, but you wanted them to be redirected to another page when they were done?  You can do just that with the Source parameter in the QueryString.  Let's say that you have a link to a form...

http://SPServer/Lists/MyList/Forms/NewItem.aspx

And let's say that you want the user to be redirected to a link when they Submit or Cancel out of that form.  All you have to do is add the Source parameter to your link, and the form will automatically redirect to whatever you set that parameter to.  For example...

http://SPServer/Lists/MyList/Forms/NewItem.aspx?Source=http%3a%2f%2fwww.egroup-us.com

You will notice that the value of the Source parameter is URL encoded.  This just means that the non-safe characters have been replaced with a set of characters that the browser recognizes (ie %3a = : ).  When the user clicks on this link and Submits or Cancels out of the form, they will be automatically redirected to http://egroup.jasonmangone.com