Agreed, Edit Layout is nice. But the last time I checked it out you could not hotkey certain things which made it impossible to remove the right hand panel for instance (and that freaking big arrow - I hated it from the start!).
XSI is a great package but that it's the most customizable is something I have to disagree on. What you can do with the Edit Layout is not really anything I can't do in Maya already - setting up windows, viewports etc. and then switch between them with a key. What I have control over in Maya however is the modelling viewports - a big cutback in XSI. They are quite static and it takes a lot of clicks to set them up, and as far as I know you can't save the setup. You should really adress that.
And you have to admit - marking menus are pretty damn smart. Especially when you can apply them to any shortcut key you want.
No I can't drag and drop via the internet in Maya, but I can't say it keeps me awake at night. I know how to copy a file to a folder and then open it. But with the crummy file browser in XSI I guess drag and drop is a blessing.
When it comes to productivity gains I guess you may be corrct in the case of animation studios - not my area of expertice. I make models for games and there XSI does not really cut it - at least not yet.
When it does however, I'll call you for a copy.