I want to open 2 excel files in separate windows to view them side by side... but each time I try, it opens them in the same window

Fair enough. If enough people tell MS, maybe they'll change it back. Mentioning it here is one way of registering your "vote". Here are some more:

Your satisfaction Matters! Let us know your thoughts about your Microsoft experience.

https://secure.opinionlab.com/ccc01/o.asp?id=yDnqREvN

MS has a very large audience, so if you want your suggestion to be acted upon you need many people to make the same suggestion. So ask your friends, fiends <grin>, enemies, relatives, co-workers, strangers on the street also submit your suggestion to all of the following locations.

Here is proof  that once in a blue moon MS does actually listen to user input about some of it’s “stupid” design decisions: http://www.theregister.co.uk/2012/05/09/visual\_studio\_11\_grey\_no\_more/

So “.. yes Virginia …”, it is worth complaining about the stupid ribbon, or other pet peeve, they sometimes pay attention.

But then again, when I looked at the “before” and “after” I don’t see much improvement!  I’m afraid this is a fore-runner for a “metrofied” Office 15.  Well, we’ll see.

Another example of MS sometimes listening is found in Outlook. In 2010 MS removed the “Unread” messages view from Outlook.  In 2013 the “Unread” view is returned.

Microsoft: Tell us what you think

http://mymfe.microsoft.com/support.microsoft.com/feedback.aspx?formid=24

http://office.microsoft.com/en-us/suggestions.aspx?sitename=CL100569831033&type=0

Office 2013 / Office 365 Preview Help Forum

http://social.technet.microsoft.com/Forums/en/officeitpropreview/threads

MS Office 365

http://mymfe.microsoft.com/Microsoft%20%20Online%20%20Services/Feedback.aspx?formID=210

Office 2010

http://mymfe.microsoft.com/Office/feedback.aspx?formID=375

http://office.microsoft.com/en-us/suggestions.aspx 

http://www.worldstart.com/ms-office-2010-putting-in-your-2-cents/print/ (it is something of a run around, but there are links to lots of good resources too)

that's way too complicated!

You work for Microsoft?!

Great. Ask the design idiots why they made it so f'n difficult to open two separate windows with two different documents on the same mother f'n screen?!

Do you jerks have any common sense in how things work in this world and why?  Whats the point of even having a site like this where a user has to edit registry to get basic use from the software that costs few hundred bucks?!

You don't deserve to be in business, and every time someone swears at your software for not working, may it cost your corporation billions of $ per month till you fail, flop and go out of business. 

Go run a fruit stand to figure out what people need before you bother hiring a development department to assemble it.