We have been playing with Lucene Search for a few days now. In general, its a fairly well designed system with different modules for indexing, quering, storage, etc. We are working with the Zend port of Lucene to PHP ( at http://framework.zend.com/manual/en/zend.search.html ). It is currently at version 0.6 and there's at least one bug that we have discovered with it thus far, its the ability to do lookup on numeric values, like zipcodes, which we can't seem to get to work. We will mostly likely switch to the original java version soon.
I did want to point out Solr ( at http://lucene.apache.org/solr/tutorial.html ), they recently rolled out a 1.0 release. It is based on Lucene, the added features are distributed search( so it can support bigger indexes which can be partitioned over multiple servers ), and also has fault-tolerancy. Another useful feature is "guided navigation", also referred to as "contextual navigation" or "facade navigation". If you are looking to roll out search for your website/application, i suggest you take a look at Solr, it looks very promising.