I have documents from several sources, which I want to present to users according to their privileges. There is about 5 sources and they can be available in several combinations. What is the best technique, to split them into several indices each holding its own source or to use + and - queries mentioned in this FAQ?

BTW, correction to answer 492401:
'The query parser always returns a BooleanQuery...'
it doesn't, you need to construct a BooleanQuery from what you have from the parser.

Regarding multi-threaded MultiSearcher mentioned in 492438: did somebody implement one?