Several of these gas holders have become defunct and have been demolished. However exterior of few has been preserved and the space within converted to a more meaningful use.
One such example is the conversion of 60 metres wide Dublin Gasworks into multi storied apartment building. Completed in 2006-07 the building now known as The Alliance Building consists of over 200 bedroom apartments which have been built within the frame of the original gasholder. The work has been carried out by developer Liam Carroll under the designs of Architects O’Mahony Pike who has retained the original frame of 1885 and created a stunning nine-storey block of apartments using the circular shape to ensure that all of the apartments have two sided views. The main bedroom and living area are located on the outer perimeter, allowing for great views over the city. The entrance hall and ancillary areas overlook the inner courtyard.
Some more great photos and info: http://www.archiseek.com/