Well, several of the issues in this post have been resolved... regrettably, the Excel issue is not one of them.
Part of the problem is that what Excel does on Windows seriously conflicts with the way window managers work on Linux. And it doesn't matter which Linux window manager is used (gnome2, gnome3, unity, kde, xfce, etc, etc, etc).
On Windows, you will get a series of tabs for Excel documents on your lower task bar:
letter | hello world | business
All pertaining to different Excel applications. Clicking one of these brings the document to the front in Excel... on Windows.
Depending on the window manager on Linux, you might get a series of indicators with open windows (Unity) on the Excel icon, you might get tabs on the bottom like on Windows (Gnome2), you might get a bunch of blank "wineloader" windows hanging out (Gnome 3).
However, clicking on any of those brings focus to Excel but never gets focus to the desired document. The only ways are to minimize the focused document within Excel and maximize the desired one... a pain, a headache, I know.
This issue/bug/symptom is not the same as the one that plagued Word and it's even harder to solve. Essentially, the way Excel does it on Windows is "naughty" and bad and even if we miraculously hacked it to work on one of the linux window managers, it would likely break functionality and behavior with the others.
I know that from a user perspective the issues seem to be the same but on a development level they are different, very different.
My apologies for this inconvenience. I too use those quick tabs on Windows. They are brilliant there and every time I switch back to Linux I want to break the keyboard when they don't work.
On the other hand, Excel is still functional with this problem. It still does many more complicated tasks and you can still work with multiple documents with the various workarounds provided. Knowing this, it becomes our task to decide if we should continue work on fixing the tab switching between documents (something our developers say is likely impossible to fix properly)... or should we make macros work better and in more situations (something our developers have been making amazing progress on)?
The bottom line, we don't have the solution for Excel. We revisit it regularly... but the fix is not forthcoming. Our apologies for the inconvenience.