What's the problem with tabs (or any other MDI)? I suddenly have two place to click to choose which application to use. We've tried fiing this problem for years. First, when we use mostly SDIs, the computers weren't powerful enough to make this a problem. When it did become a problem, we tried grouping windows together in the same taskbar entry. People hate it. They lost windows all the time. Later, we "solved" this problem by using tabbed interfaces to simplify the taskbar, but we've really only moved the problem.
Like a lot of people, I run 60-70% of my apps in the browser. Maybe more on some days. A lot of these applications are my first choices. It screws with me. Let's say I'm listening to music and I want to change my playlist. Do I go to the taskbar (if I'm listening in Rhythmbox), Go to the notification area (if RB is hidden there), or go to one of my browser tabs, possibly in another browser window (if I'm using Pandora or the like)? I can't train myself because the situation is always different?
I have taskbar buttons and tabs, then I have more tabs inside my tabs for apps like Zoho, and I have the system menu, the application menu, and quite possibly a third menu inside my browser. I can't even remember whether the web page I'm looking at is even in the web browser, or whether it's in Miro or Rhythmbos. Arrrrgghh!
Are a global menu and a tabbed window manager part of the answer? I don't know. What do you think?