I wrote a latch contention troubleshooting article for IOUG Select journal last year (it was published earlier this year). I have uploaded this to tech.E2SN too, I recommend you to read it if you want to become systematic about latch contention troubleshooting:
http://tech.e2sn.com/oracle/troubleshooting
I’m working on getting the commenting & feedback work at tech.E2SN site too, but for now you can comment here at this blog entry…