What DBA view shows users' tablespace quotas?

A user in the states has a problem with a system on his laptop. ORA-01536 - space quota exceeded for SYSTEM tablespace.
I suspect that the user he is connecting as has a default tablespace of SYSTEM. Where can I check what his users' space quota is for this tablespace?
(And yes, I'll get him to alter the user's default TBS to something other than SYSTEM.)

SQL> select table_name from dict where table_name like '%QUOT%';

TABLE_NAME
------------------------------
DBA_TS_QUOTAS
USER_TS_QUOTAS

Tycho