All details relocated from the IIS.NET website:

• IIS7 is faster and more efficient than any other version of IIS.
• With IIS7 you can manage whole Web farms from one place.
• IIS7 allows you to delegate management workload with site owners. Site owners can also remotely manage their sites and applications over HTTPS from Windows Vista, Windows XP, Windows Server 2003, and Windows Server 2008.  IIS7's XCopy deployment model even allows you to deploy applications preconfigured!
• IIS7 is much more flexible and customizable than before, allowing you to fine tune the server (including server core!) to minimize security footprint and downtime due to patching. 
• You can save loads of time by automating more tasks with the interface that is right for you.  
• If you do run into issues, IIS7 makes it easy to resolve site issues faster, minimizing down time due to that bone headed developer on your staff. 
• IIS7 includes built-in support for PHP, making it the best Web server for both Open Source languages and .NET.  You can now have a single Windows platform to host all your web workloads!
• IIS7 makes it easy to publish content securely over FTP/SSL or WebDAV!
• Windows and IIS7 are cheaper than ever with the new Windows Web 2008 product.  This version of Windows is super inexpensive and supports all the great features of IIS, Sharepoint, SQL, Windows Media server and more for Internet facing sites!
• And as if that isn't enough, IIS7 is getting better every day with new IIS7 Extensions like built-in progressive streaming and playlist support for media content, URL Rewrite capabilities, integrated database management, powershell support, and much more.