Well, it looks free to me. I'm sure the can't really charge for an OS when OS X and Chrome OS is free. However, a few things:
 
-It's only free when upgrading or buying a device that has it installed (potentially cheaper device). And it's only going to be free to upgrade the first year. If you wait more than 12 months to upgrade, it will cost you. If you build a PC and need the OS, it will cost you to get it - if I understand it correctly
-Businesses have to pay for their multilicences which will give MS a huge revenue
-They sell Cloudstorage with or without Office to everyone
-They sell Office subscriptions on their own, annual income from subscribers
-The Windows App Store will sell software where MS get a persentage from sales
-The XBox environment is integrated in the OS where MS have made gadzillions for many years already and now it looks like it's only going to expand
-Media subscription services (XBox Music etc) will be a perpetual stream of income
-Skype credits and business subscriptions, Skype is way more integrated in the OS from Win10
-Hardware like Keyboards, mouse, etc
 
If you ask me, Microsoft has set up a pretty modern way of making money and the basis of it is Windows. Understandable that they want people to upgrade - so it's free - to start using the services - which isn't free. I think they will keep making pretty good money.
 
 
Just my 2cents

Very good analysis ProjectM.

Of course the plan to make money but free is part of the paradigm now. They will still sell stuff.  It's actually a win for us and for them.

ProjectM
 
If you ask me, Microsoft has set up a pretty modern way of making money and the basis of it is Windows. Understandable that they want people to upgrade - so it's free - to start using the services - which isn't free. I think they will keep making pretty good money.
 

That was very helpful ProjectM.  It's funny to see people falling for their marketing ploy by saying "it's free" without realizing they are drawing you into an ecosystem that's clearly not.
 
 

What is REALLY interesting is to see that they are really taking on Apple's way to make money. Apple have done it this way for over a decade now and Microsoft is diving right into the same thing with a more or less self contained eco system that can be expanded on with 3rd party stuff. I'm actually in favor of this. The less time I need to test things and trouble shoot issues and all that, the more time I can spend actually using my tools. If Windows 10 holds water, it will be a pretty cool thing for Microsoft and for anyone dependant on their software. 
 
I'm still a little worried about how well it will work after Win8 felt like a smack in the face (for me), but this time, It won't really cost anything to check it out ;)