'cloud computing' is a hot term. According to the definition provided by wikipedia http://en.wikipedia.org/wiki/Cloud_computing, Hadoop+HBase+Lucene+Zookeeper, fits some of the criteria but not well.
Hadoop is scalable, with HOD it is dynamically scalable. I do not think (Hadoop+HBase+Lucene+Zookeeper) can be used for 'utility computing'. as managing the stack and getting started is quite a complex process. Also this stack is best running on LAN network with high speed interlinks. Historically the "Cloud" is composed of WAN links. An implication of Cloud Computing is that different services would be running in different geographical locations which is not how hadoop is normally deployed. I believe 'Apache Grid Stack' would be a more fitting. http://en.wikipedia.org/wiki/Grid_computing Grid computing (or the use of computational grids) is the application of several computers to a single problem at the same time — usually to a scientific or technical problem that requires a great number of computer processing cycles or access to large amounts of data. Grid computing via the Wikipedia definition describes exactly what hadoop does. Without amazon S3 and EC2 hadoop does not fit well into a 'cloud computing' IMHO
