This weekend I looked into Regain a little. This is a
desktop search tool written in java that uses Lucene.

Unfortunately at the moment it is pretty raw. It uses Swing, and
one of its dependencies uses awful reflection hacks to get at
Sun-specific classes — I think to make it possible to have an icon
show up in the Gnome notification area. Needless to say, at least the
GUI isn’t working with gcj yet.

I think the way forward is to reuse the indexer from regain but
write a new GUI using java-gnome. This looks surprisingly
simple.

Other interesting projects in this space are: Lius (additional
Lucene indexers), LucQE (query
extender), and Searchy (search
results aggregator).