I agree with Ken. The temp tablespace acts as a nice limiter on poorly
formed user queries. The only problem is because it's a shared space, your
nicely formed query that uses temp space might be the query affected by a
users malformed query chewing up lots of temp space.
Also, I've always asked for the queries that people are running if they complain about running out of temp. Sometimes, the creation of an index will will negate the need for a sort or a gathering of stats will produce a better plan.