Bingo! There's the answer I was looking for. This is true, depending upon how tight you tighten the screw. I busted some heads off in the past but today I'm pretty cautious doing so.They do get weakened every time they are torqued down. After a few uses you will find that the heads will twist off. I'll re-use drywall screws one time before replacing...they are fairly cheap...
T nuts are a pain in the *** and not needed. Just use a nice thick screw.Depends how much you take your subs out. If you do it often then I would invest in T nuts and bolts but if you do it once in a while, then I would change screws every 2-3 times you take them out. I have taken my 15" out 4 times now and have had no problems reusing the drywall screws.