Ron Guth:
The 1906 Liberty Nickel Proof is relatively common and can be found in nice condition. The mintage is slightly lower than normal, mostly because the enthusiasm that collectors had for Proofs in the 1890's wore off a little but after the turn of the century and was not revived until 1909, when the new cent was issued. PCGS has, by itself, graded over a fourth of the entire mintage of Proofs! The most commonly seen grade is Proof-64, followed by almost equal populations of Proof-63's and Proof-65's. Superb examples are scarce but show up frequently at auction. The finest example certified by PCGS (as of June 2011) is a single Proof-68 Cameo.