Here's the 24h latency data on EC2 east, west, eu, apac: http://dl.dropbox.com/u/1898990/EC2-multiple-zones-24h.png

Last 60 minutes comparison data: http://dl.dropbox.com/u/1898990/EC2-multiple-zones-60m.png

time in GMT.

A study we (Cedexis) did in January comparing multiple ec2 zones and other cloud providers: (pdf) http://dl.dropbox.com/u/1898990/76-marty-kagan.pdf