Just the other day in Portsmouth, NH, there was in incident where a GPS cache alarmed the public and the gamers were arrested. The cache they used was a metal box duct taped to an electrical box on the side of a local chain supermarket. Here is the newspaper article. Just the week before, Boston police and federal agents arrested folks that had put 'lite brite' like boxes on the bridges as part of a marketing campaign. I would have thought that would be enough to let GPS gamers know what the limits are for discretion.
A friend of mine emailed me to say how horrified he was at the arrest and he started a heated seacoast discussion online.
I have organized dozens of these GPS events in many different areas of the country both public and private. I would not want my hard work interrupted or ruined by having a cache attract attention.
Some venues appreciate the attention that they would get if teams found a cache on their property. Always, always, always secure permission. Some would not like it at all as many scavenger hunts require the participants to take photos or create a situation. Virtual caches just have the participants answer questions from the proper location.
I feel an obligation to respect the public environment that we now find ourselves in. Having fun, learning new communication skills, and moving around outside are the goals for my games at both Ultimate Treasure Hunts and Can You Find It?
It must be great fun because it is so popular.