Workspaces are a good idea, but I experience that I rarely use them. The reason, I belive, is that it takes a little work of mind to accosiate the category of my choice with an icon essentially of Opera'a choice. A solution might be custom icons (se ref below) and/or custom labels. Maybe also some kinds of tabs, or a different location, or somehow more separate from the other icons on the left toolbar, as workspaces are something more fundamental.