I used to know one, and have done a bit of reading about it. It struck me as a reversed-stupidity version of Christianity, though there were a few interesting memes in the literature.
Depending upon the Type of Satanist, yes, they are often just people looking for a high "Boo-Factor" (A term made-up by many of the early followers of a musical Genre called "Deathrock" (it's more public name is now Goth, although that is like comparing a chain saw to a kitchen pealing knife - the "Goths" are the kitchen knife).
Many Satanists, especially those who hadn't really read much of the published Satanic literature would just make something up themselves and it was almost always based in Christian motifs and archetypes...
It has been claimed on this site that the fundamental question of rationality is "What do you believe, and why do you believe it?".
A good question it is, but I claim there is another of equal importance. I ask you, Less Wrong...
What are you doing?
And why are you doing it?