Is there a way, preferably PowerShell based, to extract all the configuration data for a particular web site, for installing that web site on site at clients?
Each website on iis7 will have its own Web.Config file. That is usually all you need to deploy a site to a live server, with the catch that these files can be setup for development use (show errors, etc). If you use a professional build tool, or deployment tool then you can have two web.configs one for deployment and one for coding. But most of the time you just update your web.config to turn off error reporting and switch out database connections before copying a site to a production server.
If you are looking to export Web Server Settings. IIs does have powershell scripts to export IIS settings, and even tools like Web Farm Framework to keep multiple IIS servers in sync.
If you can be more clear on what it is you are trying to achieve, we can help you better.