Take a Vista at your stupid innards, Windows.

Operating systems are such a mess, especially ones which have been cobbled together without any forethought like Windows. In constructing an operating system from scratch, one needs to invent and adhere to certain logical conventions. Of course, there is a line between some abstract academic perfection and a usable, user-friendly piece of software, but Windows has neither. To make Windows an efficient, extensible, flexible, and robust system, the design team would have to solve the following.

The resolution mess (bitmaps/vectors, monitor size and aspect ratio)
The install/uninstall mess (make it consistent and clean)
The registry mess (why is there a registry and then still hidden local values)
The icon mess (this isn't 1988 anymore, go to an Apple Store and peep game)
The font mess (why isn't management a lot easier? why is this so mysterious?)
The filetype mess (see the previous comment)
The control panel mess (make it consistent and logical)
The ease of use/functionality mess (kill help balloons, for one)
The modularity mess (how many things should each app or service do?)
The file organization mess (why is My Documents buried so deep?)
The desktop metaphor mess (why is the Desktop inside itself?)
The local vs network mess (not enough room to talk about here)
The compression mess (ZIP, RAR, ACE, JPG, GIF, PNG, CAB...)
The storage mess (flash drives, hard drives, internet drives, sex drives)
The hardware mess (plug and play is broken)
The UI mess (make it consistent and not dumbed down, please)
The WINDOWS folder itself (just take a peek inside it)

And on and on and on. These are just things the end user battles with. What about DLLs, the GDI model, DirectX and other APIs, system "hooks," security, customization, services, codecs, DRM, legacy support code bloat, monopolistic app integration, nondisclosure of privacy issues, fragile shortcuts, Steve Ballmer, command line parameters, Winsock, UPnP, hard locks, no WinFS, bootstrapping via BIOS, activation, proprietary Java and C, .NET Framework........

I'm not saying designing a modern OS is an easy thing, especially when you're not in control of other aspects of the machine, and have to ensure interoperability with such. I'm just saying someone could do a lot, lot better than Microsoft has. Oh wait a minute, someone has. Everyone else. Why has this heap of steaming excrement dominated them all then? Oh wait a minute, they're ruthless and unethical. Well, there goes my faith in the world.