Its a very nice program. Its basically a commercial variant of ChessX ( Macintosh version of chessX at www.box.com/chessX ) with many additional features including a very nice Opening explorer and a much better player explorer as well as adding the ability to play against the computer.
Currently HIARCS Chess Explorer is the best chess application for the Macintosh. The PC version is pretty much identical to the macintosh version except with a windows look and feel.
Perhaps the most impressive thing about HIARCS Chess Explorer is how solid it is. I have been using it every day since it came out and it hasn't crashed once. Compare that with Chessbase which admittedly has many more features but which crashes regularly.
I've just finished a review of HCE. That's all there is on my new site at the moment.
http://www.zfchess.com/hiarcschessexplorer.html