MySQL stored procedures work fine when invoked from application code IME. The lack of native collection types is not ideal when you need to inject N values to a bit of data logic. As such, and for other reasons, I personally prefer raw parameterized SQL passed through a lightweight ORM that handles mapping for me as well as securely marshal a collection value into a parameterized query. But beyond that Id say that they are "usable".

Can you elaborate on the challenges you've faced with them?