Another option to serialize objects is using the XML format. It has a lot of advantages, but its not performing well. In come cases this performance aspect is only a very small part of the transaction, but since there is so much of SOAP protocols floating around, in some cases they should be reconsidered. The fastest Java XML library that I know of is StAX. I've created a matching XML to the Thrift and Protobuf schemas, limiting the tag sizes to only two chars. Makes the XML not too readable, but limits its total size.
Here are the performance charts comparing to StAX with Java plain Serialization, Thrift and Protobuf.