I believe the million point thing was given away some time back, although the 100,000 point prizes may still be out there. I have read two different opinions regarding usage and upgrades - one seems to be that using the online makes it more likely to get upgrades, while the other seems to be that using it knocks you out of most upgrades. It would be interesting to hear Marriott's take on this.
I do think there are problems with the app overall - the check-in seems to work, but the check out portion seems quite buggy and rarely seems to work for me.
It can be helpful if you would like to check into your hotel room early. The day prior to your arrival you can check in and list your anticipated arrival time. As soon as your room is ready you will then receive a notification on your phone. Some of the Marriott properties have a Mobile Check In Line which could save you time at the Front Desk.
I think it saves time. Usually there is a mobile app check in line and the most I have waited is one person in front of me. The cards are ready, typically they ask if I want to keep charges to the credit card on file and after that I am off to my room. As vaboywnder mentioned, if you want to check in prior to the published check in time, I think the mobile app will give you priority. Checked in as early as 10 AM with no issues.
Plus I want to win the million mile bonus!
The one time mobile check-in truly came through for me was when I was in Koln. I still had to wait (for the one person in front of me) to check in, but I arrived somewhere around 12-1PM. I used mobile check in as soon as I landed in FRA, and my room was ready when I got to the hotel.
The reason I'm saying it came through for me, the person in front of me was also an elite member, and he was told his room wasn't ready. He was also told there was no upgrades available, but I was upgraded to an executive suite (though I emailed the GM in advance to ask for one)
If I really want an upgrade, I also email asking for one. Alwailys say that I understand its on a space available basis and if one is not available, I understand. However I have always gotten a very nice upgrade this way. It seems like this puts you to the front of the line as opposed to waiting until check in. That being said I have gotten very nice upgrades without asking (2 bedroom suite at the JW in Summerlin NV). Unfortunately it was just me and I checked in about 5 PM and checked out about 7 AM.