i've got lighthouse running in the background all the time and regularily check the cpu usage... 3-4 times mitakuuluu was shown to be using 50% and a restart did help... if it happens, you'll notice the phone to get quite warm so for me it is easily detectable...

can't trace the reason though... has happened on 3g/4g, wifi, charger connected/disconnected, even over night... not even sure if it's down to mitakuuluu or sailfish...