I'm reading it now. I've never quite believed because it all seemed illogical. Lewis's logical approach is v ery helpful.
I became a believer at a very young age - when I was in college I never had "doubts" per se - but questioned things. Mere Christianity solidified things I'd been taught, as well as things I "found" on my own. It was a book I read that made my heart pound a little harder because it re-enforced what I'd come to believe on my own.
I enjoyed Francis Schaeffer as well - however I found Lewis to be an easier read. :)