Look for the chapter on 'Ebook Indexing" by Glenda Browne and Mary Coe in the third installment in ASI's popular "Index It Right" series. The book is available from Information Today at http://books.infotoday.com/books/IndexItRight-Volume3.shtml.
Australian and New Zealand Society of Indexers
The Indexer: The International Journal of Indexing
Society of Indexers (UK)