I do colocation as well, but if you don't have someone there to babysit your server, sometimes it can be nightmarish. It's nice to not worry about if a disk fails and you need someone to swap out one of your raid spares and hopes he doesn't swap out the wrong drive bay.
With colocation companies, everyone is sending their own custom built servers to the data center so nobody knows the exact configuration per server. If a drive fails, or a memory chip goes bad, you need someone there that knows the layout of your hardware config to debug the issue. I have a bunch of servers at RippleWeb but I'm sure the guy there has to deal with 1U servers from Dell, Tyan, Supermicro, and all kinds of other manufacturers.