Apache Lucene can be said to be one of the strong applications that can draw you towards Java land. Either you choose Java for your work or you end up writing a Java layer to make use of that. There are many applications which are not very good at search, and it is mainly because efficient fulltext search engines are not easily available. And unfortunately the search functionality does not get enough priority to build one exclusively.
Now Lucene is available in the PHP land as well, brought by Zend Framework, and it is much better than other Lucene implementations. I think it is great that now PHP applications can build their own search engines using this. The caveat is that it is PHP 5 only, while most of the PHP applications have still not jumped the divide yet.
Otherwise this is going to increase weightage of PHP amongst the candidate programming languages. And I look forward to using it in future projects.