A few thoughts from my expererience training three developers on OpenACS:
The old (pre-4.0) OpenACS/ACS classic was relatively simple IMO, and it was easier to build from first getting the webserver to return a page to using the various ACS packages and utilities. With 4.0 and greater, you encounter a lot of complexity from the get-go if you try to actually work with packages. For a sort of quick-start, I wrote some (very simple) documentation and exercises that took the group through retrieving "hello world" from the database and returning it to the browser, using only the db_ api - just to give the developers a quick look at the basics before before plunging into concepts like templates, ad_form, objects and so on. It seemed to help get things rolling.
Also, if you yourself approached OpenACS with some background web applications and UNIX, don't discount the additional things someone with a different background has to contend with. As I recall, OpenACS had a steepish learning curve for developers used to delphi/MS access.
