I think I've posted this before, but a couple of years ago when I was staying at a hotel in Florida on a regular basis I got pretty chummy with the front desk staff. They explained the process to me like this.

Each morning a list gets sent to the hotel listing all of the SPG arrivals for the day, starting with Plats on the top, Golds next, then the other levels. I was shown this list a couple of times and it ran a few pages for this particular hotel, and averaged 40 Plats per night during the week. With only 13 suites at this hotel, and no Club, suite upgrades were pretty rare.

Someone on staff then goes through the list and would assign an upgrade based on the number of nights someone was staying after guests paying for the suites were assigned their rooms. Those staying fewer nights had a better chance of getting the upgrade, and they didn't give any upgrades for partial stays - it was too difficult to manage and there were always others who they could upgrade.

I was told they would start at the top of the list and work their way down. I seem to remember thinking I was glad my name didn't start with a Z as I would never see an upgrade.

And yes, after making friends at the desk I found my upgrade percentage increased as they would recognize my name and make sure I got upgraded. But it was also day of arrival dependent - Sundays were almost always guaranteed, Mondays were hit or miss and by Tuesday all the suites were gone for the week.

So yes, it is manual with input from SPG on status. But get to know and be friendly with the morning desk staff and you'll find yourself at the head of the line. The occasional box of chocolates and a friendly smile go a long way.