Changing the subject slightly:
In the world of computers, there are programs and documents. For years now, programs were always able to open multiple documents in the same program. If you wanted to switch between your open documents, you went to the menu option and selected which document to work with.
 
With IE, Microsoft broke this usability standard: instead of keeping all web pages within one program, IE opens a new copy of itself.
Then, starting with Office 2000 (or was it '97?), Microsoft continued this trend: if you open two Word documents, you'll have two copies of Word open... instead of one copy of Word containing two documents.
They must have realized that this was causing too many open programs on the Taskbar, so they created "grouping" in Windows so all the open copies of Word would stack up on each other.
Imagine if this idea extended to all programs: if you want to work with a second Photoshop document, yep- another copy of Photoshop has to be opened. How many copies of Photoshop could you open before your computer runs out of memory and gives up? (I frequently load 10-15 files into Photoshop and run a "batch convert" action. Imagine if Windows tried to open 15 copies of Photoshop!)
Then why do users need to open a second copy of Word to work with a second Word document?
 
Personally, I think tabbed browsing is the correct way to do things: all of your web pages are contained in a single web browser and you don't have to guess which IE contains which page.
And, yes, it is faster to glance at the tabs instead of going to the taskbar, clicking on the IE group, and trying to find the page to work with.

VanishingPoint... Advanced 3D Modeling Solutions