Why the Windows Registry sucks technically (2010)
I have worked with Windows registry for at least 2 decades and it is one of the things I rally hate about design of Windows (and I like the way config files are kept in Linux). 
A very big virtual file system (with a parallel access API of its own) inside a very big (at that time, slower) file system (and its own API). I wish Windows limited its config to only pure file-system file. Simple and flat, instead of this mess of over 100 MBs which has been itself a source of many vulnerabilities. The legacy baggage is also terrible.