An odd thing about those half off certs:

One of my friends in my lab used a half-off cert (I've collected a bunch of them from generous FTers as well as through the SG program). Oddly enough, he was asked for an SG number (he gave mine) because he was using it.

Apparently, he was placed in a pretty nice room (I don't know much of the details, unfortunately) and he was given free morning beverages at the William Penn.

To make matters more pleasant, I was able to collect miles (it was a leisure stay)! [It turns out that at least a couple Omni hotels are willing to give you points for qualifying stays from friends/family - just book the rate and call the SG coordinator and let him/her know about that.

Now, if I could only figure out a way to use a stay, an upgrade cert, etc. to get into one of those multi-room suites...