I'm not sure I'd use db-transactional-serializable-migratable closures that often even if I had them (assuming the overhead wouldn't be worth the occasional "session timeout" message the user would see). Perhaps in some domains though?
Looking at clients' deployed applications, the web boxes tend to average over a year's uptime so I can't say it seems like it'd matter that much.
Provided you've got runtime code loading and a useful QA process, I don't really see why you'd need to care - MySQL's lack of transactional DDL causes far more downtime than lack of serialisation would were we using a continuation-based system.
