Ron Guth:
The 1909-D Dime has the smallest mintage of any of the Dimes produced in 1909, and the smallest mintage (under 1 million coins) since 1904. In most grades, the 1909-D Dime fetches a nice premium, but this may be an overreaction to the mintage since the 1909-D is no more rare than the other Mints of the year (based on the number of certified examples). For instance, the 1909-O has a smaller number of certified Mint State examples than the 1909-DS, yet it is almost invariably priced lower then the 1909-D. It should be the other way around.
Finding a nice, Mint State 1909-D Dime should be accomplished easiy. MS64 is the most frequently-seen grade, bracketed by equal amounts in MS63 and MS65. Gems are rare, especially in the elusive MS66+ grade. None have been graded higher.