The defining characteristic of cult vs religion is whether or not the organization attempts to alienate followers from all nonbelievers (i.e. the rest of the community at large) for the purpose of exploitation. In this light, a lot of fundamenetalist sects can be seen as cult-like at best.
Scientology is very much a cult and one that has harmed hundreds of thousands of people world-wide and Tom Cruise is a jackass for helping to further their cause.
There are theories that a lot of religions start out as cults. Mormonism certainly did, but is no longered considered one by most authorities on the matter.
Edit:
giantpinkbunnyhead said:
Hey... a fool and his money are soon parted, and the wise man puts himself in a position to profit from it. Some people will believe anything.
The reason scientologists will accept all this nonsense is because not accepting it means they have to live with the fact that they've been total larks for years and tens of thousands of dollars. That's why they don't kick things off by telling people the relgion is based on really crappy sci-fi. I think L. Ron Hubbard got a sick kind of kick out of making what higher levellers "discover" even more bizarre and outlandish the higher they get just to see how far he could push people's insane need to justify the fact that they've given everything over to the church. If I could go back in time and strangle that bastard I would, but I do have to admire how brilliant he was at selling complete and total BS to people. He was a very accomplished verbal story teller and an amazing liar.
I still love that Jack Parsons stole his woman though. Bwaahaaahaaaa. Love & Rockets. Excellent read about one of most bizarre characters in the development of modern rocketry.