I consider the 1906-D a rather underrated issue; not as much so as the 1901-S, 1902-S and 1905-S, but underrated nonetheless. It is certainly not a common date; in fact it is moderately scarce in choice uncirculated (MS-63) condition and gem quality examples, though they certainly do exist, are really very scarce. A few superb specimens exist but they are unquestionably rare.
Reportedly 12 proofs were struck (CF editor's note: see coin #89050) but only two or three can be accounted for at the present time. The only one ever auctioned was sold in Kreisberg-Schulman's Menjou sale in 1957.