Salary/hourly is a symptom, not the cause. MOST hourly employees are non-exempt and MOST salaried employees are. There are no die-hard rules, but in general in order for an employer to legally classify an employee as non-exempt they must a) supervise other employees and b) are required to make frequent decisions based upon their own judgement and experience.

My company just recently reclassified most of us non-executive exempt workers as non-exempt because is was legally safer than not paying us overtime. So now I'm a salaried non-exempt employee, which means I get pay the same thing twice a month no matter how many work days were in the pay period (generally between 10-12), unless I clock overtime, for which I get paid time and a half based on my annual salary divided by work hours in the year (2080).

Overtime in CA is defined by law as more than 8 hours in a day, instead of 40 hours per week.