Policies for Exceptions

A question to all the serious software architects here (I hope there are some!). I am currently looking to improve exception handling (currently most of our exceptions are of the standard PHP types).

Got a few questions, want to do this right....

• What policies do you use when categorizing custom exception hierarchy's?
• Do you have a collection of common exceptions you use (e.g ConnectionException, QueryException)
• How do you handle the inherent multiple inheritence issues in this field (e.g do you use IConnectionException and IRedisException on a RedisConnectionException)?

Tips? Got any resources or articles by experts in this area?

decent post: http://blogs.msdn.com/b/kcwalina/archive/2007/01/30/exceptionhierarchies.aspx

(note: exception hierarchy isn't language-specific)