I was involved a couple of years back in the London demonstrations against this cult and know more about them than I care to admit.
The problem is that they sneak their way in through the back door so to speak, you won't hear about the insane xenu story untill it's way too late.
You will never see someone offering to tell you about scientology, they will present themselves as a self help service, anti drugs program, stress help program etc...
They have been known to take advantage of disasters in order to gain new recruits, such as offering 'stress tests' around the WTC shortly aafter 9/11 and the london bombings etc...
learn more at http://www.xenu.net/
or just watch the panorama documentary by the BBC a couple of years ago here http://www.youtube.com/watch?v=QuJlZ_f1594&feature=related
it's pretty scary stuff.