"I remember having to move our systems to make sure we were in a data centre as close as possible to them and Google/Yahoo…"

Hurricane Electric comes to mind. A friend rents rack space there and I tagged along a few times when he was installing a new server, etc. Wild place. A bit of security to even get in. In one of the huge rooms where his rented rack is, 5 meters or so of racks with the same noisy hardware—"Might be Pinterest", my friend suggested.

Other racks literally enclosed within a welded wire cage…

I ended up with a host called GoGrid since they were able to offer a mix of dedicated servers and cloud for when we needed to burst and they had space in 365 Main Street SF. I went to visit their team while in town and they took me for a tour of the data centre and it was very much like that with them pointing to random racks as being owned by X, Y, and Z. It feels embarrassing to say but I was a bit star struck by the servers.