In "normal" solr usage, where Solr is the only thing writing to your index, you should never get a lock timeout ... typical reasosn for this to happen are if your servlet container crashed or was shutdown uncleanly and Solr wasn't able to clean up it's lock file (check your logs)
There is an option to tell Solr to remove the lock file on startup. On the trunk there is also an option to tell solr that it doesn't need to bother with a lock file. (i don'tremember whatthese options are called of had, but they are fairly well documented in the example solrconfig.xml) -Hoss
