I've never used MySQL, but since your structure is the same in all cases, it makes ssnse to put everything into one big database with a key to indicate which user each record belongs to. That will probably save you a lot of trouble in the long run. For instance, if you need to change the structure later, it will be a lot easier to change in once instead of 400 times. The only question is if MySQL can handle that number of records without a problem.