I had a discussion with a friend in Microsoft  IT this morning, and as we were evaluating some query plans we ran into more clustered index woes. Remember that clustered indexes affect the base table itself (which is why there can be only one) and are expensive to update. They are fantastic for reading data, but you need to carefully evaluate if they meet the criteria for having an efficient use of this type of index.

More here: http://www.sqlskills.com/BLOGS/PAUL/category/Indexes-From-Every-Angle.aspx