I use that same sort of menu in XFCE for quickly accessing a folder in a deep hierarchy, and I really like it. A lot faster than navigating through a file explorer.
That said I've used another application on Windows that had deeply nested menus, and hated it. The difference was in how the menus were implemented. The menus for this application would close if the mouse moved off the menu at all, while the GTK ones do not - they only close if you hover over a different menu item (opening it instead) or click off the menu. That made navigating the application's menus a tedious exercise in "threading the needle" with the mouse cursor.
That said I've used another application on Windows that had deeply nested menus, and hated it. The difference was in how the menus were implemented. The menus for this application would close if the mouse moved off the menu at all, while the GTK ones do not - they only close if you hover over a different menu item (opening it instead) or click off the menu. That made navigating the application's menus a tedious exercise in "threading the needle" with the mouse cursor.
I assume BeOS didn't make that mistake.