I rarely check a bag but priority handling by UA is non-existent for me when I do. Yesterday at SFO Int'l arrivals and again in NY when I finally got there my bag was in the last 3rd (estimated). I laugh at the tags because they mean nothing except make the passenger feel good and it cost UA $0.05c to buy them (just a guess). From the environmental aspect I wish UA wouldn't waste their time with such frivolous things unless they actually worked.
UA will probably send a note out to their baggage handlers reminding them of the priority tags, it'll get better for a month, and then everything goes back to the way it was.
I agree with the poster above - if there aren't priority bags on the cart to unload then go ahead and unload the non-priority bags. But the question is begged, why aren't priority bags offloaded from the plane in such a way as to be offloaded onto the belt first? It's super easy to do.
-RM