I've seen some reports with plugins loading after people upgraded their servers to 3.9.0, then 3.9.1. I have no problem on Windows 7 with the embedded database (upgraded from 3.8.2 to 3.9.1). Maybe it's linux related. What distro are you on? Also 64-bit?
As i said, it looks it runs ok on my server, though it only prints out traffic to Launcher console. I can't find a file where it prints also. There is no stdout log file and stderr is empty. Readme doesn't say it clearly, so i'm not sure how it should work.