In attempting to get Umbraco working on my development machine, I successfully compiled Umbraco-CMS-7.2.1 then created an IIS Application for Umbraco.Web.UI.  

What did I do wrong?

Here is the binding information:

=== Pre-bind state information ===
LOG: DisplayName = System.Web.Mvc
 (Partial)
WRN: Partial binding information was supplied for an assembly:
WRN: Assembly Name: System.Web.Mvc | Domain ID: 3
WRN: A partial bind occurs when only part of the assembly display name is provided.
WRN: This might result in the binder loading an incorrect assembly.
WRN: It is recommended to provide a fully specified textual identity for the assembly,
WRN: that consists of the simple name, version, culture, and public key token.
WRN: See whitepaper http://go.microsoft.com/fwlink/?LinkId=109270 for more information and common solutions to this issue.
LOG: Appbase = file:///C:/dev/umbraco/Umbraco-CMS-7.2.1/src/Umbraco.Web.UI/
LOG: Initial PrivatePath = C:\dev\umbraco\Umbraco-CMS-7.2.1\src\Umbraco.Web.UI\bin
Calling assembly : (Unknown).
===
LOG: This bind starts in default load context.
LOG: Using application configuration file: C:\dev\umbraco\Umbraco-CMS-7.2.1\src\Umbraco.Web.UI\web.config
LOG: Using host configuration file: C:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet.config
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework\v4.0.30319\config\machine.config.
LOG: Policy not being applied to reference at this time (private, custom, partial, or location-based assembly bind).
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework/v4.0.30319/Temporary ASP.NET Files/umbraco/43bd052d/2fb87ff6/System.Web.Mvc.DLL.
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework/v4.0.30319/Temporary ASP.NET Files/umbraco/43bd052d/2fb87ff6/System.Web.Mvc/System.Web.Mvc.DLL.
LOG: Attempting download of new URL file:///C:/dev/umbraco/Umbraco-CMS-7.2.1/src/Umbraco.Web.UI/bin/System.Web.Mvc.DLL.
LOG: Using application configuration file: C:\dev\umbraco\Umbraco-CMS-7.2.1\src\Umbraco.Web.UI\web.config
LOG: Using host configuration file: C:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet.config
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework\v4.0.30319\config\machine.config.
LOG: Redirect found in application configuration file: 4.0.0.0 redirected to 4.0.0.1.
LOG: Post-policy reference: System.Web.Mvc, Version=4.0.0.1, Culture=neutral, PublicKeyToken=31bf3856ad364e35
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework/v4.0.30319/Temporary ASP.NET Files/umbraco/43bd052d/2fb87ff6/System.Web.Mvc.DLL.
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework/v4.0.30319/Temporary ASP.NET Files/umbraco/43bd052d/2fb87ff6/System.Web.Mvc/System.Web.Mvc.DLL.
LOG: Attempting download of new URL file:///C:/dev/umbraco/Umbraco-CMS-7.2.1/src/Umbraco.Web.UI/bin/System.Web.Mvc.DLL.
WRN: Comparing the assembly name resulted in the mismatch: Revision Number
ERR: Failed to complete setup of assembly (hr = 0x80131040). Probing terminated.