"The fastest growing religion (in terms of percentage) is Wicca -- a Neopagan religion that is sometimes referred to as Witchcraft. Numbers of adherents went from 8,000 in 1990 to 134,000 in 2001. Their numbers of adherents are doubling about every 30 months."
The survey points out that figuring numbers on the pagan population is notoriously difficult, as it is an "underground" religion, whose proponents often keep a very low profile to avoid attacks from an uninformed public....so in other words, the numbers above are most likely lower than actual figures.
Also interesting to note a 9.7% drop in those identifying as Christians over the past 11 years.