JISC has produced a range of studies and guides looking at virtual learning environments, a selection of which can be found below:
JISC CETIS article - VLEs at the heart of curriculum innovation (Feb 2011)
UCISA VLE Surveys (latest version published 2010)
JISC CETIS Distributed Learning Environments: A Briefing Paper (Feb 2010)
Distributed VLE programme (due to complete Dec 2011)
Supporting Education in Virtual Worlds with Virtual Learning Environments (due to complete in June 2011)