You have to be using the mod of pcmanfm for the home_folder in main to work:http://igurublog.wordpress.com/downloads/mod-pcmanfm/
Depending on how you install it, you may need to run "pcmanfm-mod" rather than pcmanfm ( check the About window to see if it says MODIFIED VERSION). Also note that the normal version of pcmanfm (0.5.2) will remove the home_folder setting from your main config file (it doesn't recognize it and will omit it when saving the config file).
And home_folder=FOLDER must be in the [General] section. Once that is done and you restart pcmanfm-mod then it should work.