My church went through the book together several years ago. We did the entire program, churchwide. My pastor preached the sermons, all the S.S. classes used the lessons (from preschool through adult), and we ended with a huge "ministry fair" to find areas of opportunity to serve.
I loved it! And so did my entire church (about 1200 members). One of the neatest things was knowing everyone was studying the same thing at the same time. All those who were reading the book daily were reading the same thing. All the classes were teaching the same lesson on the same Sunday, and the sermon tied it all together.
People were really excited about it, and we had an unbelievable ministry fair at the end where lots of church members were made aware of (and signed up for) ministry opportunities they may not have previously realized were available.
About a year later, we did "40 Days of Community", and what an awesome experience! We all came together as a church to do "acts of kindness" in the community...and I was amazed at all the things people thought of to do to minister. Classes got together to do things, and what was especially neat was seeing the student group discover things they could do to serve others in our area. They came up with things they could do at school (and other places) just to show kindness to others.
I firmly believe that going through the study as a church body was what made it so successful for us. Everyone had the same focus, and it was outstanding!
The book is not a deep theological textbook, and I don't think it was written to be such. Personally, I read a chapter a day as a devotional, and I thoroughly enjoyed it. Some of it was very basic for me and I enjoyed being reminded of the "basics" in a fresh way. But there were also things in the book that really made me "think deeper", and gave me a new perspective on some familiar passages and ideas.
I know there are many, many people who don't care for Rick Warren or his book, but I'm not one of them. I saw my church come together more in the 40 days than it had been in a long time. I saw people excited about serving. I saw new people coming to church and being saved as a result of what the study did for our members.
As Tater said, "Let God guide you and get out of this study what God will show you. Any time you are seeking, He will show you something." I know from experience, you will receive a blessing from churchwide participation, if it is bathed in prayer, and if it is approached "expecting" a renewal from the Lord.
CJ