Lucene in Action is very well written. I liked the presentation of code samples as tests and found almost no fluff. If you don’t have a background in information retrieval (I don’t) I think you’ll enjoy this book for the background information on IR that is thoroughly integrated with the text even if you have no plans to use Lucene (though you’ll obtain an itch to use Lucene, it’s so simple and powerful).
One non-technical comment I made about Lucene in the Etech talk is that it may be another open source category killer. As Apache eliminated much of the opportunity to sell HTTP servers, I suspect Lucene will eliminate much of the opportunity to sell embedded search libraries (which seems somewhat significant judging by the quantity of ads for same in programming magazines).