Let's see... on my current Linux install my root drive (no user documents or settings) is 9.5GB.
I have..
* A full office suite
* An email / calendar program
* A bitmap graphics program
* A vector graphics program
* A general diagram tool
* A diagram tool for making GUI mockups
* A UML modelling tool
* A mind mapping tool
* A project management tool
* A selection of different media players, each tailored for a purpose (music, video)
* A CD ripper
* A CD creator
* A DVD / video transcoding application
* A webcam app
* A photo management app
* Two different web browsers
* More than three different text editors, all with features that blow Notepad.exe out of the water
* A backup system
* Database management tools
* The tools for three different version control systems
* Development kits for C, C++, Ruby, Python, Perl, XML, Java, C# (probably missed some out)
* Two Java development environments
* File differencing tools
* A hex editor
* The thoroughly awesome GNU tool set which by itself makes you more productive with a large folder of text files than anything else
* Encryption software
* Archive tools for every common archive format and most of the uncommon ones
* Several sets of remote desktop / system management tools
* VPN software
* A Windows-compatible file server
* A sticky notes program
* A BitTorrent client
* A unified instant messenger client
* A specialized IRC client
* Skype
* A unified social network client
* A cloud folder with 5GB of complimentary storage
* A calculator
* A few desk toys
* A typing tutor
* The usual system management widgets
* A means of pretending to be Windows when the need arises
And
* A package management system that keeps ALL of it up to date (not just the operating system)
* and doesn't need a reboot every time it does it ... No, I don't think 40GB of Windows provides all of that.
(no, not all of this came out of the box, but all of it was available for free, and all of it fits in that 9.5GB ; there's some "payware" on there too but I didn't include it above)