I cant provide a solid answer on this, but I went to search google because I was curious about it to and on the 20th or so page of results, this link came back:
http://www.isse.gmu.edu/~lili/642/Servlets.pdf IF you search that document for "serialized", it makes reference to if more service requests are recieved than the connection pool allows, then the requests are serialized (following this particular model). I dont know if this has any relevance to your question, but its an instance where servlet serialization is used..