Many people claim that autism is on some sort of WILD upswing, and is an epidemic of sorts. While I cannot say if there is a rise or not for sure, one thing is quite certain: The autism spectrum is much more understood in this day and age. We are able to correctly identify someone as autistic as opposed to mislabeling them as troublesome, distant, aggressive, impulsive, etc. There is a certain selection bias involved with the autism diagnosis increase claim.
An interesting bit of news saying that scientists have actually identified the gene that can be traced to 15% of autism cases. That's good news in many ways. First of all, it further confirms that vaccines are not involved. Also, with our better understanding of genetic therapy, we may be on the road to figuring out more effective treatment for autism (As opposed to chelation and other dangerous quackery).
An Interesting article on some possible connection to Vitamin D and autism: http://www.sciam.com/article.cfm?id=vitamin-d-and-autism&sc=DD_20090424 I would caution reading too much into this though since it is very preliminary. After all, there have been correlations of autism with linoleum floors too!
While on the subject of autism causes and information, there is also the "baffling" correlation to folks who have vinyl flooring. Keep in mind, correlation is not causation... That's the same bad reasoning that got hold in the pro-disease community. Scientific American has also run an article on a possible connection to a Vitamin D deficiency. Of course, on the same page there is a link to an article talking about environmental factors causing autism. While overall the jury is still out on this, we are starting to find some of the myriad of interrelated factors that can play into it. One thing we do know though is that it's NOT vaccines that play into that particular myriad.
I also can't help but to put out a warning and admonishment to people. Don't try to look for the simple answer. All over the internet, I see parents and debaters attempt to simplify autism as to being caused by X or Y and say that's the end of the discussion. Most of the time, the people who do so are laypeople who have no scientific training, so I can sort of forgive them. However, we live in an incredibly complex and dynamic world. Almost nothing is simple anymore. It really is imperative that the responsible citizen get at least some amount of scientific literacy. Otherwise they will continue to be simpletons looking for the simple answer.
Science is pretty cool though. We don't have answers to something, so we look into it, and then we find it. We don't make up fairies or pixies, but use what we know and delve into it more. It's almost as if Science Works!