If personal experience has any weight then yup, it's true. All of the non-Christian men I've had (consensual) sex with have been ten times better in the sack than the Christian ones. The Christian guys had the whole guilt thing going on, and it wasn't the kind of guilt that can be sexy ("ooh what if we get caught"). It was that self-esteem-crushing, "I'm a bad person for doing this" kind of guilt that killed their confidence and made them nervous and awkward. I had one guy break down after we had sex for the first time because he felt so guilty.
People shouldn't feel guilty about wanting to have sex, whether in the confines of marriage or not. It's a completely natural thing and (if you're doing it right), it feels good. Unfortunately, most Christians are guilted about sex for almost their entire lives. From infancy until I broke free of Christian circles, I was told that anything sexual was very, very bad and that I needed to be modest and not masturbate and remain pure. In high school I heard so many horror stories during chapel time of women who had sex before marriage and how it completely ruined their lives. Even if I hadn't been abused, I probably would have been terrified of sex anyway just because of all the things I was told my entire life.
The Christianity I grew up with lays the guilt on real thick when it comes to sex, and it shows.