I try not to rely on Singleton, however I prefer decoupling to not using Singleton. Thus, I often use Singleton coupled with the Prototype pattern, which allow for registering the Prototypes at library load (global objects construction).
I am writing a server consisting of a number of libraries. There is a number of "common" libraries, then one library per service. A "main" library is tasked with the purpose of looking at the message received and invoked the right service depending on a key... This uses a simple std::map.
Using a Singleton for the map allow me to have totally decoupled code. No library depends on my service library, no line of code outside my service library is tasked with registering its service. In fact, it is such that I can decide which services are embedded simply by altering my "link" command at compile-time: if I do not link with a library, its service is not embedded.
I really find it useful there... for configuration and such I prefer to use the MonoPattern: ie normal looking class with all instances sharing the same data (thus wrapping a real singleton). Makes for easier migration just in case it's necesary since the clients don't know they are using a Singleton undercover.
