I have the April 2006 version of the plugin installed. If I set the GENPDFADDON_TOCLEVELS to 0 to disable the TOC, it has no effect and the TOC appears with the default levels. If I set GENPDFADDON_TOCLEVELS to 1 or 2, the variable is used and it limits the TOC to the appropriate level. If I set the URL version of the variable 'genpdftoclevels' it also has the same behavior as I just described.
I have determined the problem is in GenPDF
.pm. The problem is due to incorrect parsing of the options due to an 'undef' variable being equivalent in perl to 0 in a conditional. I will be checking in a corrected version shortly.
The checkins fix this item and updated the documentation. A new release of the plugin has been uploaded to the Plugin web.