Here are the differences from http://www.mywindowsclub.com/resources/3302-Key-differences-between-IIS-IIS-Developer.aspx.
If you already have IIS installed – its a better product. IIS express would only be used by people who don’t have access to IIS or want something that is lighter than IIS but more like IIS than Cassini.
- Integrated with OS
- IIS 7 ships with the operating system and is tightly integrated to Windows.
- IIS developer express is a separate downloadable tool
- Targetted users
- IIS 7 is for both developers as well as for production purposes.
- IIS developer express can be used only for development purposes and not for production.
- Supported Windows editions
- IIS 7 will work only on Windows Vista and newer editions of Windows. In case of server OS, IIS 7 will work only on Windows 2008.
- IIS developer edition will work even on older version – starting from Windows XP and newer.
- Process model and activation
- In IIS 7, the worker thread is automatically launched and managed by Windows Process Activation Service.
- In case of IIS Express, user has to handle this.
- FTP support
- IIS developer express does not support FTP while IIS 7 supports it.
- WCF support
- IIS Developer express supports only WCF over HTTP.
- IIS 7 supports WCF including over TCP, Named Pipes, and MSMQ.
- Multi developer support
- IIS 7 is a single user application.
- IIS Developer express supports multi developer environment. Configuration files, settings, and Web content are maintained on a per-user basis.
- Visual Studio integration
- All editions and versions of Visual Studio have built-in support for IIS 7.
- Only VS 2010 and future versions will have built-in support for IIS developer express.
- Runtime extensions
- IIS developer has support for URL Rewrite and FastCGI.
- Webmatrix offers support for SEO, database management and Web Deployment. Other extensions that are offered with IIS are not yet tested with IIS Developer express.
- Management Tools
- IIS 7 is managed using the IIS Manager.
- IIS Developer express can be managed using Webmatrix. Also, the express edition has support through system tray.
- Port used by IIS
- The default website comes with IIS 7 listens to port 80.
- The default website part of IIS developer express listens to port 8080 to avoid conflicts with IIS 7 when they are running side by side.