Just thought I'd pass on some info I just discovered. I've been successfully using the CVS head version of Lucene as of about 2 months ago. I then got the formal release (1.4-rc3) and tried it with my application, but it failed. I tried it with some commandline test routines and they worked fine, but not my application (runs under Tomcat 4.1.24, on a Windows XP/Pro).
After a lot of debugging, I discovered that IndexReader was trying to create a lockfile in a non-existent directory (called "temp" at the same level as the index directory). After I manually created this directory, everything seems to be working fine. (Why this happens only with the Tomcat application, and not commandline apps, I don't know. Probably has something to do with JVM properties.) Regards, Terry