I installed Duplicator on my WP site running 3.4.1. When I activated the plugin, it came up with the message:
The plugin generated 277 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin.
However, I was able to generate a package without any issues, so presumably I can ignore the warning?
BTW, I had WP-SuperCache enabled when I activated Duplicator. Not sure if that was the cause of the conflict or not.