The 1868 Gold Dollar is a common date relative to other dates in the series, but it is not as if there are hundreds of Mint State examples floating around at any given time. In fact, Mint State examples tend to be low-end, as evidenced by the higher populations of PCGS-graded MS61 to MS63 examples. Fortunately, a sufficient number of high-end examples exist to satisfy collector demand. The PCGS CoinFacts Condition Census starts at MS66, includes a few MS67's, and finishes off with a couple of amazing MS68's.
Most 1868 Gold Dollars show a shiny, diagonal streak connecting the right side of Liberty's bust with the rim to the left of the final A in AMERICA. This was a Mint-caused anomaly in the die and should not be confused with a post-strike defect.