string testSerialize = JSON.serialize(database.query('SELECT COUNT(Id) custTot, Industry Indus from Account Group by Industry'));
system.debug('test '+ testSerialize);
Ran this query in developer console Spring 13 both sandbox and production results in producing the below output
[{"attributes":{"type":"AggregateResult"}},{"attributes":{"type":"AggregateResult"}},{"attributes":{"type":"AggregateResult"}},{"attributes":{"type":"AggregateResult"}},{"attributes":{"type":"AggregateResult"}}]
Before Spring 13 it returns data after this upgrade causing problems.