I think you actually hit upon the main problem with the ribbon in your defense of it. The ribbon is in fact a great replacement for the old toolbar system and so, when you sit and spend the time to customize the bar, just like when you used to customize the toolbar, you are going to work faster.
However, as a general purpose tool for finding commands it's awful. It relies on you already not just knowing the command you are looking for, but that you know what the shortcut to it looks like. Worse, sometimes those commands are buried under other commands.
I do a lot of work in autocad, and while %90 of what i do I do on the keyboard or on the tool-bars, but there are hundreds of commands, many I simply don't use on a regular basis. All I usually need to find the command is to go to the menu of related commands, and read the short descriptions of the functions there. That's what the menu is there for, to provide some insight for the available commands and that is not what the ribbon provides.
I shudder to think of having to provide me grandmother with instructions over the phone on how to do something where I have to explain to her toolbar icons rather then just telling her the command she is looking for. Fortunately, she's still on windows XP.