Mapping custom attributes between Leads and Contacts

As  most things in life, rather trivial if you know how to do it. Still something that pops up a lot on the web in newsgroups and communities.  When converting Leads to contacts/accounts all ootb attributes are automatically mapped. Now how can you map also your custom attributes?

You just go to the Lead entity, look under 1:N relationships, "contact_originating-lead" and then "mappings".