Lucene 4 has some great improvements in autosuggest/autocomplete,
e.g.AnalyzingInfixSuggester.
GroupingSearch and JoinUtil are other nice ones.
It would be interesting to see blog writeups on leveraging these new
features through HSearch.
Joins should imho even be considered as candidates for inclusion into the
querybuilder. Grouping might also be considered as a kind of projection
perhaps.