Fifty years of research has shown that relative to simply interviewing customers 1:1, group techniques for ideation — focus groups and brainstorming — are harmful, as they:

1. Reduce the number of ideas generated, and
2. Reduce the quality/originality of the ideas generated.

Griffin and Hauser in “The Voice of the Customer” show that even the cost argument doesn’t work. But still these idea-slaying methods continue to wreck havoc with innovation projects in corporations as consultants promote their “expert moderation” and senior executives find them fun.

So it is worth sharing the words of a former high priest of focus groups, who confesses his past sins: 

http://www.promisecorp.com/blog/?p=82

Several of the academic researchers, including Fern and McQuarrie, who have debunked focus groups over the past half-century have also been former expert-moderators.

(also see past postings on customer research methods)