I read an introduction to a website that was three short sentences. The first sentence was a question, the second a very clear and short (in other words, excellent) description of the site, and the last one was a link to learn more. It was wonderfully done.

But I had to read the whole thing 2 or 3 times before I got what the site was about. Why? Because that first question I actually had to ponder. So my mind was working on an answer while I kept reading; and as a result I didn't process what the next two sentences said.

Morel of the story: when writing your webcopy don't ask anything thought provoking. Asking a question for your first sentence is a very good idea so long as the user doesn't have to think to answer it.