There have been several attempts in the past to have South California become its own 51st state. It is very unlikely to be successful because doing so requires the approval of the voters of California, the Congress, and the President.
Since South California would undoubtedly become Republican, Democrats will be apt to squashing any such plan.
Jeff Stone is a Riverside County Supervisor that is pushing for this to be a part of the November ballot in California. They have launched the website CaliforniaRebellion2012.com.
And I would support it if it were ever on the ballot.
The last post they made was back in Mid-2011 so it is hard to know the progress of this.
But here are my opinions of it. I am from Southern California and I whole-heartedly support breaking off into a 51st state.
Here are the benefits as I see it.
California has 55 electoral votes. By being split up, it allows the more Conservative southern part of the state to become a new battleground state.. winnable by the Republican.
Management. Being split into two separate states would lend itself to being better managed.
More Freedoms. The liberal policies of the north (via taxation and regulation) have scared away jobs to Texas, Arizona, and New Mexico.
Immigration. The liberal north controls the way the state handles immigration.. but it is the south that has the bear the brunt of the impact. Let the new South California handle these issues.
Jeff Stone says the new South California would be run with little taxation and an simpler regulatory environment. This would make doing business in the state a lot easier and I support that.