Yes, custom fields are easy:
<step>
<title>Importing custom fields</title>
<detect>{$from_prefix}custom_fields</detect>
<destination>{$to_prefix}custom_fields</destination>
<presql>TRUNCATE {$to_prefix}custom_fields;</presql>
<query>
SELECT
id_field, col_name, field_name, field_desc, field_type, field_length,
field_options, mask, show_reg, show_display, show_profile, private,
active, bbc, can_search, default_value, enclose, placement
FROM {$from_prefix}custom_fields;
</query>
</step>
<step>
<title>Importing custom fields data</title>
<detect>{$from_prefix}custom_fields</detect>
<destination>{$to_prefix}custom_fields_data</destination>
<presql>TRUNCATE {$to_prefix}custom_fields_data;</presql>
<query>
SELECT
id_member, variable, value
FROM {$from_prefix}themes
WHERE variable LIKE 'cust\_%';
</query>
</step>
added to /Importers/elkarte1.0/smf2-0_importer.xml following the XML structure. 
Less easy may be the instant message fields (ICQ, AIM, MSN,
), but... honestly... is there anyone still using any of them?