It's a strange way to submit entries in a scavenger hunt, we grant you, but government bodies are not known for their elegant uses of social media. The advantage to this method is you can figure out exactly how good odds are of winning something, if you have too much time on your hands, by sifting through the Visit Denver Facebook Wall.
As it turns out, we have too much time on our hands: There have been 21 submissions thus far by our admittedly very lackadaisical count. There are 13 prizes to be had, among them airfare for two from Southwest and a night at the Crowne Plaza, as well as a bunch of gift certificates to restaurants and free admission to various cultural institutions. You can see the complete list right below the list of scavenger hunt activities.
So right now, you've got better than 50/50 odds of winning something. Considering that, if you live or work anywhere near downtown, you're probably going to walk/drive directly by six of the things on that list in the next two days, you might as well enter.
Not to sound too cynical. This could be a fun way to see some stuff you've never seen before in your own city. After all, it tends to be the things right in front of your face that you wind up overlooking.