When you register to Glu.fi service, you can tell your reason for registration. Most of the registrants tell their reason and for most of them it's celiac disease.
Glu.fi is Finnish based and there are approximately 29 000 (12/2010) diagnosed celiacs in Finland and when that reading is compared to the number of Glu.fi's users with celiac disease, you'll find out how many percentage of them uses Glu.fi service.
Notice that anyone can add any kind of content into service. Also all advertised products are not gluten-free. Administrator is not responsible and you take full responsibility what you eat. If you notice vandalism or contents that include gluten, please notify the admistrator.