Since it's late, I'm not going to give proper sources but you could probably find them if you really wanted from this:
http://www.sciencedaily.com/releases...1008131852.htm
There's also a beautiful study that I cannot find for the life of me right now.
The amount of mercury in vaccines is too low to have a causal link. Mercury levels are similar in children developing with autism and children developing normally. Of course, let's just ignore all of the environmental sources of mercury that children are exposed to that nobody is blaming for autism because we're focusing on vaccines. It's no coincidence that the association between autism and vaccines came about because autism tends to be noticed/diagnosed around the time of immunization for measles. This is because the measles vaccine tends to be given around the time where autism shows up, and we're sort of wired to look for patterns.
Jenny McCarthy, obviously a worried parent and you can't fault her for that much, is just part of a terrible trend of celebrities promoting bad, harmful science. Measles is going to do much worse to a child than the vaccine ever would, and now we're seeing more and more measles cases because of people not vaccinating for this terrible reason or religious ones. I don't mean to offend but if you're in the position to give people advice about these sorts of things, it's irresponsible to spread this kind of misinformation, particularly when it can be harmful.