I installed GlassFish 3.1.2 Open Source Edition on my Windows 7 box and wanted to manage the GlassFish instance from Eclipse 3.7 using the GlassFish server runtime plugin.
I installed the plugin via the eclipse marketplace and found out that the version from the marketplace doesn't support GlassFish 3.1.2.
So I googled around and found out about this blog post describing how to install the GlassFish server runtime plugin properly on Eclipse 3.7. There is also a great stackoverflow question describing the problems with multiple "internal GlassFish servers" each time you start Eclipse after you have installed the server runtime plugin for GlassFish 3.1.2.
The later problem only occurs on Windows machines!