Nice to see another ubuntu user of personalbrain aboard! Like you, I use the same brain on a dual boot computer with Ubuntu 11.10 and (sometime) win7. It works really great. Drag & Drop in Linux works with the "mucommander" file manager. After some research, I went to the conclusion that the lack of drag&drop feature in PB comes from JAVA. Drag & Drop between linux applications and java application (not only PersonalBrain) does not work; unless implemented in both applications. By the way : another tip I'd like to share : you can link virtualthoughts in both environment to the same thought ( ex : c:\temp (win7) and /mnt/temp (linux). Then, when you are under win7, you see the win7 virtualthoughts; and when you are under linux, you see the linux one. This way, a shared directory in both environment can be used seamlessly with the brain...
TheBrain 9.0.250 - OsX High Sierra & Win7