As I was reading docs on Andrei's new memcache extension (memcached) I came across a binary serialization extension called Igbinary written by Sulake Dynamoid Oy. This extension promised much more optimal serialization routines by using binary, rather then a clear text format. Sounded, good so I decided to run a few benchmarks on it.
He uses several different sizes of files to run his tests and found that, while it is just a bit slower than the normal serialization, the compression rate that's about fifty times smaller than the usual. The extension also offers a "compact_strings" parameter that allows for even more compression of just string data.
As you can see the serialization speed is pretty amazing, once your serialized data set is in excess of 100bytes, you can expect nearly 2x improvement with a ~30% data set reduction with igbinary. I think we got a winner!