$20 trick at hotels?

Does anyone have experience with attempting to get a room upgrade with the $20 "sandwich" at check in? A lot of forums make it out as an almost sure shot, but I wonder if it's really that simple. I ask because I'll be hitting up TI in July (check in on a Saturday) with 4 other guys (2 rooms), and was wondering what kind of chance we had at getting two upgraded rooms on a weekend, or if that's kooky talk.

There is a $20 thread here and a link to another website here.

It's completely doable at any property in Vegas (including the Wynn) and if it is denied, they normally give the money back to you. The hotel staff are obligated to show the $20 to the cameras above to show that they didn't steal anything. The $20 is, in my opinion, the best $20 you can spend in Vegas. At the worst you will get the money given back to you, at best you will be given a much better room than you booked that had you booked online would have cost you much more than the $20 you spent.

I wonder what would happen if you slip them a $100? Think you'll get an even better upgrade? Or the same one for $80 more?