We are getting fully reproducible hangs in NetBeans under Merlin build 76. 
Please, download some development build from:
http://www.netbeans.org/downloads.html#builds
from "Development Build" section - e.g. today the build is marked "NetBeans-dev-200108210100.zip"


Two scenarios how to "hang" the IDE follows:

1. Start NetBeans fresh build
2. Click just "Finish" button in [Setings Import Wizard]
3. Press 2 times "Next" button in [Setup Wizard] dialog, so you will be switched to "Module Installation"
4. Try to change by (mouse clicks) values of some property panels in "Enabled" collumn - from "True" to "False"

-> property panel will not be expanded -> leads to hang (full thread dump attached)

OR:
1. Start NetBeans fresh build
2. Click just "Finish" button on [Setings Import Wizard]
3. Click just "Finish" also in [Setup Wizard] dialog
4. Open some file by double click on it in [Explorer] - e.g. /sampledir/examples/texteditor/Ted
5. You will be switched to "GUI Editing" workspace
6. Click on "[JFrame]" node in [Component Inspector]
7. Try to change the name of "title" property in [Component Inspector] - click on "Ted" by mouse to do so

-> textarea will be enabled and then the IDE will hang (thread dump attached as well)

Try both descriptions under JDK 1.3.1 to see it's working well.