I realize this question is from 2013. However, I had a very similar issue today. The error message was:
ERROR: Couldn't determine $SPLUNK_HOME or $SPLUNK_ETC; perhaps one should be set in environment
I installed Splunk as follows: First, I had extracted the tgz archive on my Linux system via sudo. Then I chowned the directory to the splunk user. Then, I ran "/opt/splunk/bin/splunk enable boot-start -user splunk" via sudo. Then, I tried to "splunk start" as the splunk user. However, I received the error message above.
I noticed the following permissions on the file /opt/splunk/etc/splunk-launch.conf: