if you want a crystal only solution
bring in all data
group on user
insert a summary at ther group level as the max of the date field
maximum({system_usage.usage_date},{table.user_field})
now you can do a group selection criteria on that result
maximum({system_usage.usage_date},{table.user_field})<dateadd('d',-60,currentdate)
Note that group select criteria leaves the groups in the tree and exlcude s them in a later pass for the body of the report.