This summer while checking out possible new data centers, one our eval outings our team visited was a former telephone crosslink site. It was over in Shawnee. That site HAD 48V DC and a significant DC bus system installed. There was lots of shiny copper and an impressive power / UPS room.
On what could connect to it. Looking at the options, I think some of the HP ProLiant systems have Telco versions that can be fed DC rather than standard AC power supplies. One in particular, the HP P-class Blade servers has external power sources and they feed 48V DC into the chassis. HP even has a rack power setup that can stack multiple blade chassis and tie it all to a 48V system or a common AC/DC supply to stack them.
You DON'T want to drop a screwdriver across it or you WILL see stars.
Fred Armantrout Burns & McDonnell Engineering Co.