I have a CCK Content type called "Job". I attempted to add a custom link to these Job nodes called "Apply For This Job" using the Custom Links module. In the query string section I entered:

job=[field_job-title]

[field_job-title] is a token provided by the CCK module that appeared in the Placeholder Tokens section of the custom links setup page. When I actually went to view a node, the custom link appeared, but the query string was not being filled in correctly and the query string at then end of the link just ended up being:

?job=[field_job-title]

Bottom line is the "Job" content type did not include a field_job-title field, so it did not get replaced. That was a field used by another content type. So watch out. Just because the token shows up in Placeholder Tokens section does not necessarily mean the token is available in the context you are using the custom link for.