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If I set JDk 1.7 as the default JDK (with java preference pane - checked on cmd with "java -version") and try to start Netbeans 7.3 than netbeans always hangs when starting the "background project scanning...". If I set the default JDK back to 1.6 than all is fine. For some reason other application only using JDK 1.6 and not 1.7. I will try on a fresh installed 10.8.2 machine if other application also hangs (no JDK 1.6 installed).
Please attach a thread dump (http://wiki.netbeans.org/GenerateThreadDump). Most likely a known problem of JDK 7u7 on OS X. Try to download http://jdk7.java.net/download.html 7u10 b10, it should be fixed there.