Who should read it: It is for you if you are looking for a quick overview of this topic for a project, an interview, or in general.
What is an aspect: WAn aspect is a common feature that is scattered across methods, classes, or object models. This gives a way to encapsulate some qualified behaviors. An example of such behavior is logging or exception handling. AOP compliments OOP (Object Oriented programming). Aspects enable modularization of concerns such as logging that cut across multiple types and objects.
What are common implementations: Some common implementations of AOP are Spring framework, Jboss, and Aspect J. AspectJ uses Java like syntax. It has its own compiler. Jboss is an open source Java application server. It has its own AOP framework. Spring uses XML based configuration for implementing AOP. It uses annotations which are interpreted by AspectJ library, for the purpose of parsing and matching.