Serialization of a method means that calls to the method are
handled one at a time. A serialized
method cannot have more then one
thread operating on it at a time.
Serialization is the enemy of scalability. A serialized method is like a grocery store with only one register open. If there are six people waiting to check out, then it will take close to six times the amount of time for the last one to finish then it would if six registers were open.
However, serialization does have its place. Java's Synchronization offers a way to serialize threads' access to a method.