Greenwich Mean Time is not the world's time. So said Dr Felicitas Arias, director of time at the International Bureau of Weights and Measures, on the Today programme this morning (listen again here). GMT has been a standard in Britain since 1847, but since 1972 most of the world has operated on Co-ordinated Universal Time (UTC). Apparently GMT is not accurate enough, nor is it uniform, since it reflects the speed of rotation of the Earth, and the Earth rotates at varying rates. Atomic clocks, on which UTC is based, are more accurate.
I must say that I've noticed that there is often confusion if GMT is used when I am talking to someone in another country. Until I knew better, I found that someone elsewhere would agree to Skype me at a certain time -- 14:00 GMT, for instance -- but, in fact, we were often an hour out and never got to speak. That is because many people think that GMT is the current time in the United Kingdom. It isn't. The time in the UK at the moment is currently GMT+1; we call it British Summer Time. We put the clocks back at the end of this month and we will be on GMT again over the winter.
The OED gives four pronunciations for Greenwich: /ˈgrɛnɪtʃ/ (Grennitch) , /ˈgrɪnɪtʃ/ (Grinnitch), /ˈgrɛnɪdʒ/ (Grennidzh), and /ˈgrɪnɪdʒ/ (Grinnidzh). It gives the US pronunciation as /ˈgrɛnɪtʃ/ (Grennitch), the same as the first of the four UK pronunciations. The pronunciation of Green... as 'grin...' is more old-fashioned, I think.
For the interview with the director of the International Bureau of Weights and Measures, click here.