HA, failover and load balancing / howto?

I have some web applications and rich clients that need to
geographically localized copies (for network latency reasons) of a
database (East Coast, Central, West Coast and Japan) These will be
mostly read however there will be full CRUD activities going on. I
think this means that there will be a cluster in each region to deal
with load and single failures and when a whole region perhaps dies,
clients will fall back to another region.

ex:
4 servers for load East Coast
- db and webservers
4 servers for load Central USA Coast
- db and webservers
4 servers for load West Coast
- db and webservers

The web applications (Java, tomcat, ejb3, jboss4, php) If one one, or
more web or db servers die, the others in the region are still used (ie:
just 'degraded') If all the db servers die in a region, the web server
and applications will hit the db servers in another region)

How can all of this be setup and configured and how can failed db
servers be brought back online and updated to sync into the clusters?

Also looking at the pro/con of doing this in Postgres vs mysql