Well, bitcoin is very unstable so I'll say it's not that reliable when it comes to being a payment service. It certainly can be used as an alternative payment method, especially for big transactions, but both parties should be able to trust bitcoin completely.
It's volatile, but it isn't really that volatile on a small, hourly level, and often even daily. You're unlikely to lose -- or gain much -- making day to day transactions expect for those anomalies where it falls by hundreds in a day, but those are luckily rare.
i think transactions are slow..when they make superfast transactions then it be more practical, obviously
When was the last time you made a transaction (if you have at all)? Bitcoin is lightning fast these days and payments are practically as good as instant.