Thanks Jmen: The threads in an aluminum head can be stripped out during routine plug removal if the plugs have been in there awhile. I think I'm going to take my own advice and pull the plugs on both my Toyotas ('05 and '07) and apply the
Anti Seize Compound to the plug threads ASAP.
I've never had them out yet since new because the mileage is low. Around 21k miles on the '07 Tacoma. NB