However I chose Fremont because it's the closest datacentre they have to Australia. Most of my readers are here.
(see http://www.linode.com/speedtest/ for pingable hostnames of servers in each DC + speedtests)
If you do want to move, you can put in a ticket and they can move you between DC's with no downtime I believe or just replicate your instance and switch IP's.
However I chose Fremont because it's the closest datacentre they have to Australia. Most of my readers are here.