I ask as i was on a Spey beat a few years ago and the gillie was setting up my rod... when i picked up my rod i saw to my horror he had cut off the loop off the polyleader and had used a knot to tie the tippet material to the polyleader
I use Orvis Polyleaders all the time - factory loop goes to the fly line and at the other end I always add a tippet ring and put a tiny dab of glue over the knot. Just add tippet to suit. These last me for years.
But the same thing happened to me as James' story above... was blethering to friends on the bankside while the ghillie very kindly set up my rod for me. When I inspected it to start fishing I realised he'd whipped off the tippet ring and tied a loop in my Polyleader!
I could almost hear him muttering under his breath: "We'll be having none of that tippet-ring nonsense around here, sir!"