I'm on 4.7 with a Macbook 2.16ghz w/ 4gb ram and 10.5.6. Hasn't crashed once for me and I've left my computer on with C1 open for at least 4 days now while editing a shoot with about 450 Canon 5D MK2 files. Also have Photo Mechanic, Safari, Chicken of the VNC (remote desktop app) and iTunes open, for what it's worth.