Althogh the tags certainly don't always work, I've had enough experiences with my bag being in the first few off the belt since I became Silver that I know they work sometimes. As an example, I flew ABQ-MDT-ABQ and ABQ-LGA-ABQ earlier this month. Arriving in MDT, my bag was about tenth off the belt; returning to ABQ from MDT, it was about fifth. Arriving at LGA, bag number three, returning to ABQ, bag number 1! These were all very full flights, and having my bag come off that early that consistently does not seem like chance.
Certainly there are times when my bag comes off in the middle or towards the end of the bunch. My theory is that some handlers care about priority tags and make an effort to get them out first, but others don't. In ABQ, which has a small staff (only two flights in and two out a day), I've really noticed a big difference with the priority tags.