JDK 1.7 Developer Preview is available for download (75 MB).It seems like the JDK 1.7 installation is not automatically set in the path. You cannot set it with the Java panel as default. After setting it from the command line NetBeans 7.1 starts (opens, parses the projects etc.) with JDK 1.7 with 8 Java EE 6 projects about 5 seconds faster (20%), than with JDK 1.6.
The UI (colors) are not consistent, but some components like e.g. the progress bar do look nicer. Try it and give feedback / submit bugs.
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