As with the bug https://bugzilla.samba.org/show_bug.cgi?id=4274
the createcomputer option is still undocumented and can only be found in svn comments.
Even more importantly, it is broken in version 3.23d.
What happens is that it uses the createcomputer option as it's own argument.
Linux-006:~ # net ads join createcomputer="Resources\Worstations" -U sup-astevens
Failed to pre-create the machine object in OU createcomputer=Resources\Worstations.
It appears to be trying to join the workstation in the location "ou=createcomputer=Resources,ou=Workstations" which, offcourse, does not exist.
This is fixed in SAMBA_3_0, so it should be in 3.0.24. I will warn you though, that "\" is used as an escape character, both by net and ldap, so believe it or not, it has to be quadrupled to work out...yes, quadrupled.
I'll add a comment to the docs, which are there in 3.0.23d, by the way, in the command itself. I'll also verify the manpages.