Good question, we did consider using #, the main benefit of which would have been that diffscuss files were still legal diffs.
Against that benefit was the consideration that there could have been comments that weren't diffscuss threads in a diff, and that would have meant that you could have legal diffs that would have terribly confused any diffscuss parsing.
Add to that the fact that you can get a legal diff back just by piping a diffscuss file through a single grep -v, and we decided not to use # (which I think was probably the right call--overloading comment syntax for functional stuff always creeps me out a bit anyway).
Against that benefit was the consideration that there could have been comments that weren't diffscuss threads in a diff, and that would have meant that you could have legal diffs that would have terribly confused any diffscuss parsing.
Add to that the fact that you can get a legal diff back just by piping a diffscuss file through a single grep -v, and we decided not to use # (which I think was probably the right call--overloading comment syntax for functional stuff always creeps me out a bit anyway).