I think IrishMammyto2 is spot on, it really is about the people involved. For starters, if your man is not clean, oral sex would smell worse than cleaning the toilet. Both partners have a basic responsibility to be clean and smelling nice.
Beyond that, why do it? Well, it is certainly pleasurable for your partner as it offers different sensations compared to sex and his own hands. Also, it can be fun both giving oral sex at the same time (69) because the pleasure your partner is feeling gets translated into the way he pleasures you and you create this whole virtuous circle which leads to a climax.
Also some people like doing it for the fanstasy involved (of just being plain dirty).
Others enjoy the control they get when giving oral sex. You are 100% in control of the speed, the technique, everything. Your partner is at your mercy and this can, for some be a big turn on.
Maybe it's just that it creates variety as it is hard, IMHO, to satisfy all the needs of intimacy just through kissing and penetrative sex.
Also, thanks 3catstoo, I appreciate your support. I definitely think these conversations have their place here, as long as they remain respectful and courteous. It is the very virtual nature of these boards which do in fact allow the conversations to happen as everyone can lose their inhibitions and talk honestly and frankly about any subject.