Tough one. The solution above is clever and made me laugh a lot; it stems from the understandable desire not to hurt someone's feelings. But really, it depends on the friend. If it's someone you respect and whose taste you have time for, next time don't read the book. Your taste in books is a highway to your soul, and if you find you hate this loved book, your opinion of this respected friend will change. (You could tell them the book is part of a big pile and you’ve got it to look forward to). But if you're really close friends, consider telling them, with tact and delicacy, exactly what you thought. One of the joys of friendship is being able to have aesthetic differences. Maybe friendship isn't often about a frank exchange of views, but if only it were…

All you have to do is be subtle. Don't make up an elaborate scenario...just say "it wasn't really my taste, thanks for recommending it, though." Move on to different subject.

Say it just wasn't quite your type and suggest a book you love to her -- that will probably put her in your situation and you won't have to talk about books anymore. Or, better yet, she'll be challenged by it and ask you for more suggestions which means you've opened her up to a whole new world of reading that isn't childish and boring.

Be honest! Depending on how close you are, of course! Miss A: "So how did you like the book?" Miss B: "Actually, I thought it was boring. It's not really my thing, I prefer xxx." Or, if it's a work freind or someone you're not too close to... Miss A: "So did you like the book?" Miss B: "I liked xyz about it, but to be honest, I didn't like it that much, I prefer xxx."

Tell your friend the book was 'incredible'. You don't have to add incredibly childish and incredibly boring. Pre-arrange to have your mobile telephone ring at that moment. Or failing that kind of sophisticated synchronisation, you can trip and fall over.