I agree with Koen. The KimballGroup states that 5 to 15 dimensions is usually the most common range and that is at the PHYSICAL LEVEL. The only thing I would add is that 3 role playing dimensions based off the same PHYSICAL dimension do not count as anthing more than 1 dimension within the context of Kimball's statement.

For example, if there is an order date, shipping date, and payment date based of the same physical table, DimDate, this is considered one (1) physical dimension with three (3) logical roles.

All of this said, I have seen situations in Healthcare where 20 - 25 physical dimensions have been justified, but, more often than not, if you have more than 15 physical dimensions, chances are you may need to go back to the drawing board.

http://www.kimballgroup.com/data-warehouse-business-intelligence-resources/kimball-techniques/dimensional-modeling-techniques/centipede-fact-table/

Kimball's official quote is this:

"You’re nearing the practical limit on the number of dimensions when you’re

approaching 15 to 18 dimensions. If your design has more, consider

combining correlated dimensions into a single dimension."