Perhaps we could share the pain and get it done more quickly.
Many months ago a few of us upgraded a production client from an acs3.2 base to acs4.0. At the time I asked Mike Bonnet to write up a summary of the work (which he did most of). For what it's worth, you can read about it at
http://grumet.net/random/mikes-migration-guide/.
I haven't looked over much OpenACS code lately, but I suspect the bits about migrating users and groups will be relevant. There was also some weird incompatibility with ns_adp_parse/ns_adp_include and the templating system that we never figured out (perhaps you have?). Anyway, hope this helps.
