I just don't get this insistance on control over utility servers. If we take sensitive businesses out of the equation there's really no argument for it. How many times has gmail been down for me? Never. What about exchange/lotus notes? At least once a month. And even when they work they're shit.
Things like email retention and recovery are two big features regarding control that I don't think Google gives you (at least last time I looked at it).
When you're using gmail, you also dependent on the internet connection. And my opinion, for business email, having abc@yourcompany.com looks better than abc@gmail.com