I have space with G4. They house about 60-70% of NH's DSL and T connectivity, colleges, businesses and have A LOT of tier1 and 2 backbones in there building. With peering to all. when they purchased more than 50% of vitts assetts there company blew up.
I wouldn't call there facility a data center its more a telco environment. It's not maned 24/7 and they dont offer hands and eyes if there is an emergency off hours unless you have key card access to the facility.
Since I moved in there december I have had 100% uptime. The speeds are amazing and staff is more than amazing.