This hasn't really affected my enjoyment of Lewis' works. Mel and I also love Narnia and we can't wait to see Prince Caspian in the theatres (subject to babysitting too!)
It just means that I wouldn't use Narnia as a way to teach concepts about Christianity to somebody. You could still point out ideas in Narnia that draw from Christianity. But I wouldn't use the Narnia stories to draw conclusions about Christianity - I think this could be a natural inclination since in many ways the Narnia stories are very similar to ideas and events from Christianity.
So, we enjoy Narnia for what it is, a fantastic set of stories set in a wonderful world with characters that we grow to love.