Depends on the severity I think. They were discussing this on the news (might've been the Today Show). I think they try to "fast-track" the ones who aren't major/violent offenders. The drug sellers, gang-bangers, muggers, assaulters, etc do the time, but the ones with DWI's etc get out early to make room for the bigger fish that need frying.
SO yeah, if you are going to get a DWI or get busted with a few ounces of coke, do it in LA!