I will give you a clear answer: I switched from Windows to Linux quite a while ago, and I do everything with Linux that I used to do with windows, and more. Specifically, this is what I do with Linux:
Internet browsing with Firefox (also available for Windows)
Email with Thunderbird (also available for Windows)
Instant messenger with pidgin (also available for Windows)
Develop software, specifically LAMP apps (Linux, Apache, MySql, PHP), as well as c++ work. You can do this on Windows, but I find it to be more robust and easier and faster under Linux. I know this because I spent many years developing software with Linux. Now I do it exclusively with Windows. There are things I do with ssh and scp with Linux that is a serious pain to do with Windows, but very easy with Linux.
Play games - all kinds of games - Sims, Tomb Raider, all versions, with Wine or Dosbox, minecraft, Steam, Valve's lineup, Metro redux (native linux version available), The Witcher 2 (native linux version available), the list just goes on and on and on.
Office - Libre Office is awesome. I despise what Microsoft did to Office. Libre Office is what MS Office should be but isn't anymore.
It isn't what you can do, it is what you can't do. And I can't think of anything I can't do. I don't use windows anymore, I have replaced all of my Windows installs with Linux. And I don't miss it.