Singleton Design Pattern Questions

Singleton Design Pattern is the basic design pattern that most of the developers seems to learn at the very early stages of their career (including me). So it is natural that there are lot questions that interviewers asked in order to see whether the person has just crammed up the definition or actually knows how to write it as well. Also, the implementation of this pattern has also changed a lot over time and a thorough knowledge of the same would mean that the person is also up to date with the new techniques.