Interestingly, enough, I used miles to purchase a ticket for my son and the reservation allowed me the ability to use a GGU. I didn't use it because it's a shortish flight and doesn't seem like a good value, but I was surprised I even had the option since award tickets aren't supposed to be eligible.

Also, we are halfway through the year and I haven't used any of my GGU's yet. Like others have stated, I really wish there was more space available and they were easier to use.