Ron Guth:
The 1848-O Half Dime does not have the highest mintage of the O-Mint Half Dimes from the 1840's, but in terms of the number of certified examples, it is exceeded only by the 1840-O varieties combined. Most of the Mint State 1848-O Half Dimes appear in MS-63 to MS-66, with the highest population appearing in MS-64. The finest example certified by PCGS (as of February 2012) is a single PCGS MS-68.
Fully struck examples are rare, as most show weakness on the denticles and/or on the AL of HALF and the I of DIME.