Great plugin! I needed to retrieve the email address, first and last name for all the registered users on my site who checked an extra-field box marked "thisweek"... The SQL is a bit tricky, but here's how I did it:
select id, user_email,
(select meta_value from wp_usermeta where
meta_key='first_name' and wp_usermeta.user_id = id) as first,
(select meta_value from wp_usermeta where
meta_key='last_name' and wp_usermeta.user_id=id) as last
from wp_users where
id in (select user_id from wp_cimy_uef_data where
field_id=(select id as field_id from wp_cimy_uef_fields where
name like "thisweek") and value like "yes");