I'm not saying what the point of a BB will be for other people . Personally, I'm perfectly happy with Gmail app - I don't see the point in having mail thrown at me every minute of the day, so a 20 minutes interval is more than enough for me. I can even quit the app so I will not be disturbed by new mail all the time which isn't even possible with BIS as far as I know (-> work-life-balance???).

Besides: BIS isn't instant most of the time either. With Gmail or Yahoo, it might be for some people but I read many complaints about delays here, so...