I do not check bags that often but over the last couple of years have had good luck with my priority tagged bags on AC being among the first bags out. Latest examples:
- IAH to YYZ end of October by the time we had cleared the short Customs line our bags were waiting for us.
- FRA-YYC a week ago, waited perhaps 5 minutes after using my Nexus card to quickly clear customs.
The only time I find the priority tags are ignored is when I check my skis.