I tried to update my 1.6.2.14 installation to 1.8.0 last weekend. Unfortunately there is a problem with the pbx_spool.so module under OS X, which causes a 100% CPU load right at start, independent of whether asterisk is actually doing something or not. I temporarily disabled the module in the modules.conf with noload => pbx_spool.so , and now everything runs fine…
Maybe somebody should have a deeper look at this module once again.
If it isn’t, make sure you have compiled with optimisation disabled, then use gcore to get a core dump, whilst it is showing the symptom, and follow the procedures in doc/backtrace.txt, before submitting a new issue.