The first time you try to start the logstash-web service after installing, you will see the following error:
"logstash not configured to start, please edit /etc/default/logstash"
After editing the abovementioned file and attempting to restart the service, I got the same error message. It turns out you actually have to edit /etc/default/logstash-web.
Recommend the error message read as follows instead (for clarity):
"logstash not configured to start, please add START=true to /etc/default/logstash-web"
logstash-web is removed from 1.5.0 upcoming release. Kibana 4 must be used separately