exchange in house or at co-lo

As critical as exchange is, and with things like DR/BC, uptime, Security, remote users, etc. to worry about,how many of you keep your exchange in house vs. at a co-lo?

we have the option to do either, our users are somwhat distributed. i’m leaning towards co-lo. it’s always up, remotely manageable, etc.

your thoughts?
I say Co-lo all the way.