ORR, you beat me to it! I too was going to create a Signal Hill challenge since it is the high point of Arkansas. That might be one draw back, since there are no distance restrictions there could be an limitless number of challenges in the same spot or for the same thing. Like the free market system I think that Groundspeak must be hoping that the "supply" and "demand" will help determine the market. I placed my challenge as a photo challenge for the Logan County Museum and I have another I will publish tonight that will be a photo challenge at the Arkansas Coal Miner's Museum here in Paris.
I also downloaded the free app on my Droid X (believe it or not there are complaints on that too). The app only does geocachingchallenges, but that is great for me since I don't cache with my phone (I do use it to go paperless). The app was free so I have no complaints.
Another complaint was about those who log them without actually completing them. Who are they cheating? No one but themselves. I know I have audited logs for some physical caches that I have placed that were logged online but they didn't sign the cache log. I suspect they never really found the cache, but then again they are living the lie, not me.
I for one want to thank Groundspeak for adding something new and not being closed minded about it. I'm sure with time they will address any major issues and tweak it to work better. Again those who complain about them will make the most noise.
I have to note I saw in the Groundspeak forum where one cacher actually disabled one of his caches because someone included it in a challenge without asking his permission. I looked at his cache listing and he even threatens to archive the listing if the challenge isn't.
I am also looking to see how challenges can be incorporated into events. For example, the Cache Mania event in October I might have a Geocaching Challenge for those who find all the geocaches placed for the event.