How is the latency? All mainstream chat apps have low-enough latency that a live conversation feels fluid and natural, whereas I frequently encounter situations where I have to wait up to five or ten seconds for an email to come through. That kind of latency would kill the experience IMO.

in my experience the "latency" for a person to reply to a message is always higher than the latency for a message to arrive. in fact, some latency is good. gives you a break to think.