Using Hydrogen 0.9.3
It would be great to select notes in the pattern editor, the same way I can select patterns in the song editor. Sometimes I want to delete 10 sounds in a pattern and I have to do it one by one. If I had a selection tool it would be easier; I would just have to select them and then press delete.
Another thing that would make the selection tool really powerfull would be the ability to combine selections by pressing ctrl or shift (like in cubase or in file browsers)