I've seen the same thing on my Mac OS X 10.6.8 installation of Ripley. Debayer takes forever, several minutes for each image. Under PI v1.7.X it takes all of two seconds for each image. I'm still looking at what may be causing this, I'm going to move everything from my earlier installation out of the Application directory and try another installation.
One other issue (so far), the update for the new documentation fails unless PI 1.8 is at the root of the Application directory. As a first trial I had placed v1.8 in its own directory below Applications but that didn't work when the update tried to run (reported error, can't find necessary files/resources). I then moved v1.8 to the root of the Application directory and the update seemed to work.
Here is an update, it took 425 seconds for PI 1.8 to debayer ONE image. I'm running on a Mac Pro (2x2 2.66GHz Xeon, "Woodcrest" the first processor to support SSSE3) with 10GB DRAM.
Another update, it seems that it is the Debayer process/icon itself that is slow. If I attempt to open a RAW file directly the speed seems reasonable (a few seconds, with the DSLR_RAW format preference set to VNG). However, if you attempt to debayer a file using the process icon it can takes minutes for the debayer to complete. This means that any workflow that requires the debayer process is effectively unusable under Mac OS X.