First thing I'm going to say is: don't only use threads like this one to make your decision. Go and talk to parents at the school or, on an open day or a tour of the school, take the opportunity to talk to the older students. Threads like this really attract a lot of people who feel very strongly about Steiner - usually negatively, but also the rare nutjobs who act like Rudolf Steiner is the messiah.
Steiner schools are honestly not religious - I've just graduated from one, and I have an understanding of all religions equally. Regarding Anthroposophy (if I've spelt that right...!) I don't really know what it is, but from what I've just seen on wikipedia, the only bits of it which have been present in my school life are the bits which encourage respect for the planet, yourself and all people.
Steiner schools don't suit everybody, but I think if you're undecided, it's worth giving them a chance. I know of some people who put their children in the school until class five, when they were moved to a State school so that they cold get ten GCSEs etc. This really is an option, as by this age you're at exactly the same level as state school children. Although Steiner children don't get formal reading lessons until they are seven, when they have learned the alphabet and the sounds they are usually capable of reading novels etc. within a year, judging by my experience (myself, many siblings and cousins and the rest of my class at school).
Most of my friends from school have recently moved to the local sixth form college, and we all agree that at the Steiner school we studied subjects in far more depth and with greater understanding - the emphasis was on learning and experiencing rather than memorising the information necessary to pass exams.
If you're worried about academics, then I don't think you need to be. At my school, the average GCSE mark was an A and in the past two years, four students (out of around thirty five) have gone from the local sixth form college into Oxford, Cambridge or UCL. Universities and colleges do recognise the merits of Steiner education and are more than willing to accept Steiner students.
However, all Steiner schools are different, and whilst I think that what I am saying is true, it might not apply to your local school. I think the best way to find out about the school is to take your children to the school events (summer/advent fairs) and talk to parents and students informally. This way you will get to see your child's potential classmates interact with each other and also be able to get a more honest account of the school.