Had a connecting flight through MIA and was forced to gate check a bag (somehow my hardshell rollaboard didn't fit in older 737 overhead). I was flying first class and FA promised it would be delivered at the jetway in MIA. Connection to next flight was 1 hour.

Got off of the plane and stood at the jetway until all pax deplaned. FA called to gate asking about bags. Gate agent came down and explained that the MIA ground crew aren't contracted to deliver gate checked bags to the jetway or gate. At this time I found out my flight was delayed anyways so I had time to go to the baggage claim and retrieve my bag. But if it were a heavy travel day I would have been screwed. Another couple traveling internationally were forced to gate check even though there was space in the overhead (as they found out when they boarded). Needless to say they weren't happy either.

Moral of the story, don't gate check bags to MIA if you can avoid it!