Building and cleaning Visual Studio projects from Explorer

I tend to have lots of project directories and sometimes I just want to build or clean them.
Rather than opening each solution in an instance of Visual Studio, I added items to Explorer's right-click menu. It doesn't look particularly elegant yet, but it works quite well:
Windows Registry Editor Version 5.00

@="\"c:\\Windows\\Microsoft.NET\\Framework64\\v4.0.30319\\msbuild.exe\" \"/maxcpucount\" \"/target:build\" \"%1\""

@="\"c:\\Windows\\Microsoft.NET\\Framework64\\v4.0.30319\\msbuild.exe\" \"/maxcpucount\" \"/target:clean\" \"%1\""

Blocking and unblocking downloaded files on NTFS

A downloaded file that is protected (»blocked«) by Windows because it is potentially unsafe can easily be unblocked using Explorer's Properties->Unblock.
But how does it work?
The security zone is stored in an NTFS Stream called Zone.Identifier.
$ more < file:Zone.Identifier
The Stream has the usual INI format. This is how to create one manually for a random file in order to block it.
$ echo [ZoneTransfer] > file:Zone.Identifier
$ echo ZoneId=3 >> file:Zone.Identifier
To see the streams present on a file you can use dir /r.
$ dir /r
04.09.2012  12:49                13 file
                                 28 file:Zone.Identifier:$DATA
I haven't found a way yet to actually delete a stream, but they tell me PowerShell 3.0 is going to be able to do it, or you can download a separate tool from SysInternals.