If you’re building a website in UTF-8 (all stuff: db, html, etc) you proabably can get the following PHP Notice:
Notice: iconv() [function.iconv]: Detected an illegal character in input string in ... plugins\sfLucenePlugin\lib\vendor\Zend\Search\Lucene\Analysis\Analyzer\Common\TextNum.php on line 56
This is caused by lack of information in the installation guide of the sfLucenePlugin.
Few minutes of Google-ing could brought you the following:
try to add in config/search.yml:
index: analyzer: utf8
This line solved this problem for me, hope for you too.