Paul is right, Hibernate Search uses Lucene for all the "full-text search stuff", so expect the same performance from it. Hibernate Search really unify Lucene features with the Hibernate programmatic model.
Particularly in Hibernate Search 3.1, we did a lot of work on optimization and our tests show no noticeable overhead of Hibernate vs Lucene (on comparable usages).
If you ahve performance problems, chapter 9 if Hibernate Search in Action is dedicated to the subject
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