I was one of those people who took lonely planet books everywhere, all over Europe, to Iceland, the Philippines, Cuba and now Delhi. I trusted the brand so it was the only book I brought, big mistake.
I'll only speak for Delhi because thats where I spent two weeks. So I hope this specifically helps travelers to Delhi.
The restaurants were pretty much awful, the hotel prices were wrong, the massage treatment place recommended so out of the way that it cost the cost of the massage to get there and back. I was working so I only wasted my weekends following the book. My work lunches were at far better restaurants and a aimless walk in the daytime in Old Delhi was far better than any guided tour. I also didn't appreciate the tone of this book and how much time it wasted on smug reviews and lame humor.
I think the individual country books depend really on the authors/editors, the other lonely planet guides I have were of great help. For India(or Delhi at least), try another title.