SlickEdit's file tabs are an interesting hybrid. In VisStudio, you can select "Tabbed Documents" or "Multiple Documents" -- essentially, SDI or MDI. In SlickEdit, it is always MDI, but with tabs, too.
I suspect the people that want multiple rows of tabs don't have scores of buffers open at once; the rows of tabs wouldn't leave any room for the buffer windows....
While I don't do much editing in VisStudio, I do like the interface. When you select 'Tabbed Documents", you can create several "Tab Groups", giving you a sort of MDI-with-tabs. One of the best features of an MDI is being able to look at two regions of the same file in different windows; VisStudio's splitters let you do that. (Windows->Split Horizontally| Vertically in SlickEdit)
As for scrolling tabs, I'd prefer a scroll bar to the arrows, but that's more screen real estate. (A scroll bar gives you some indication of how far from the end of the row of tabs you are, while the arrows don't.) I like VisStudio's solution: a button that drops down the list of tabs not currently visible.
So, I'd like to see something very much like VisStudio 2005. If multiple rows of tabs are what gets implemented, I'd like the number of rows to be user-configurable; when there are more buffers than can fit on the available tabs, I'd like a button to list the rest of the buffers, and avoid scrolling altogether.