When to consider a singleton

You basically want a singleton when you are sure it is never appropriate to create more than one instance of the class per assembly, yet you require an instance for one reason or another (derivation, easy serialization, properly representing a model). And singletons can ease implementation as only the type needs to be defined and no instances need to be created manually.

[meesternadim]

What do yo do for a living? Prabably programmer, but give us some more info on what you exactly do.