One of the clearest and most concise explanations of this concept I have found was at a blog named Knight of the Mind:
Based on a doctrine called "The Inferior Defeats The Superior" when roughly translated from Chinese, this doctrine calls for the Chinese military to develop a series of weapon systems that enable it to neutralize the C4I advantages of a superior, more modern, military force so that the battle can occur on a lower technology battlefield.
Additionally, it seems that Mr. Jason E. Bruzdzinski of MITRE has done extensive research of the topic, presenting his results in this testimony and this briefing (PDF). I'm glad to see that not everyone is settling for:
What actually classifies as an "assassin's mace" weapon is unclear.
-FY04 Report to Congress on PRC Military Power (PDF)
No one seems to know for sure if ShaShouJian is a weapon, a doctrine, or an RD&A program. Bruzdzinski's briefing supports the notion that this is a PLA research program seeking to find any weapon system that will give them a leg up on the United States militarily (which seems similar to earlier discussion of "pockets of excellence"). I find this to be the most likely explanation of ShaShouJian. It isn't a weapon or doctrine, but rather a program aimed at finding the silver bullet that they know they need if they seek to compete with the far superior American military.
Update: The 2005 Report to Congress on PRC Military Power again mentions ShaShouJian. The Jamestown Foundation, however, determines that the concept isn't all that unique:
Leveraging one's advantages while exploiting enemy weakness is not a unique insight into the conduct of war. While "Assassin's Mace" weapons are often perceived to be exotic technologies, such as high powered microwave weapons, electromagnetic pulse, or maneuverable warheads, the Chinese consider a much broader range of weapons to be "Assassin's Mace," including fighter bombers, submarines, anti-ship missiles, torpedoes, mines, nuclear weapons, and even rapid runway repair equipment. One American observer quoted a PLA officer that sha shou jian can be "whatever the PLA needs to win future local wars" [...] In this regard, the Chinese concept of "Assassin's Mace" is not that remarkable.