... it is because the staff at Dreamhost is dealing with an attack on their system at present. Here is their latest update:
Distributed Denial of Service Attack causing networking issues on SEVERAL machines
Posted (September 30th, 2011 at 9:01 am PST) by mir
Our initial calculations were off. This outage is impacting more machines than we anticipated. If your machine is down at the moment, you are likely affected by this outage. Sorry that I could not provide a list of all machines.
Our admin team is working on the matter and hopes to have it resolved in the very near future. We’ll keep this post updated as information becomes available. Please note that the servers themselves are not compromised (this sort of attack utilizes exploits of outdated applications installed by users to launch an overwhelming number of data requests which bogs down the networking on the servers involved – the distributed nature of the attacks make them very difficult to fix as it’s not just a matter of blocking a single IP or IP range).
Update Sept. 30th, 9:30am PST: Our admin team is still working feverishly to resolve this issue as quickly as possible (unfortunately the nature of this sort of attack is causing it to take longer than we would like). – John