To get JDK 7 up,

• I downloaded the JDK from Oracle. They have a nice dmg file, which makes it easy to install. 
• After reading their installation instructions and running /usr/libexec/java_home (which I didn't even know about), it still wasn't defaulting to JDK 7.

Surgery required.  So, I headed over to:

/System/Library/Frameworks/JavaVM.framework/Versions

This is where the system jvm's are stored.  You'll notice a symbolic link for CurrentJDK.  It probably points to:

/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents

You're going to want to point that to the new JDK, which java_home tells us is located in:

bone@zen:/usr/libexec$ /usr/libexec/java_home
/Library/Java/JavaVirtualMachines/jdk1.7.0_09.jdk/Contents/Home

So, the magic commands you need are:

bone@zen:/System/Library/Frameworks/JavaVM.framework/Versions$ sudo rm CurrentJDK
bone@zen:/System/Library/Frameworks/JavaVM.framework/Versions$ sudo ln -s /Library/Java/JavaVirtualMachines/jdk1.7.0_09.jdk/Contents/ CurrentJDK

Then, you should be good:

bone@zen:/System/Library/Frameworks/JavaVM.framework/Versions$ java -version 

java version "1.7.0_09"
Java(TM) SE Runtime Environment (build 1.7.0_09-b05)
Java HotSpot(TM) 64-Bit Server VM (build 23.5-b02, mixed mode)