Same experience as deasys, running OS X 10.2.8. My Address Book has only 250 entries. MacDialer consumed almost all CPU, the Quit menu item didn't have any effect, cmd-opt-esc to force-quit wasn't available, shutting down was the only way out. Tried it twice, same result. Trashed it, everything back to normal. Something badly wrong here. Use ABDialer instead, functions are much the same as MacDialer, except it works.