Go to http://jdk7.java.net/macportpreview/ for the download.
A list of open issues can be found here.
I as an eclipse fanboy am also happy about the release of Eclipse Indigo SR1 which adds full Java 7 support. Go here to see what is new for Java 7 in Eclipse Indigo SR1.
To use newly installed JDK in Eclipse, you have to add the path to the JDK home manually. Start Eclipse with JDK 6, select "Installed JREs" -> "Add.."->"Standard JVM". Enter the path to the /Contents/Home folder inside the installed JDK bundle and provide a meaningful name:
Have fun while trying out the latest Java 7 features!
