Development directory structures

[Guy]

Is there a concensus as to how to install all the different tools,
jars, app server, code etc for ease of maintenance and/or deployment?

For example, do you typically install everthing under a common
directory like java? I've seen people include the jboss, jdk, struts,
ant along with projects all under one top level directory.

Or, do you install all the tools to their default directories under
the root?

Any good reasons for doing it one way over another?