I've done many spilt stays and always (even when I have a car) have Disney transfer our bags and groceries. I have never had anything but fantastic service. The latest our luggage has ever arrived is 5. It's normally closer to 3:30.
Like pretty much every other business interaction, negative reviews/comments about Disney's luggage transfer service outweigh the positives without taking into account the vast majority of people who are satisfied and don't bother to comment. Human nature is to complain, not praise.
Now, do things go awry occasionally? Yes, of course. But it's a very, very small percentage of the total number of bags transferred every day.
I will actually be doing yet another luggage transfer tomorrow morning.
Steve