I have personally designed enterprise data warehouse dimensional models for 7 insurance carriers and currently working on number 8. On average our customers are maintaining approx. 15 different dimensions on how they analyze their business. My current design will incorporate close to 50 dimensions in order to allow their actuaries to perform detailed rating formula analysis.
Typically, we store all policy and claim transaction detail at a very low level. We then design fact tables around the different subject areas. They could be loss analysis (i.e. Incurred losses, LAE, ULAE, outstanding reserves, paid losses, etc.), premium analysis (i.e. written premium, net written premium, earned premium, unearned premium, inforce premium, etc.) and policy analysis (i.e. inforce policy count, policy count, etc.)
Obviously, there are differences in the dimensionality when analyzing claims vs. policy related measures. When calculating a loss ratio, for example, only the common dimensionality between the earned premiums and incurred loss is useful during analysis.
I would be glad to share any other experiences...