Scientists are not the only ones who are hunting for new species. Animal and plant collectors too, searching for new exotic species to add to their collections, pose a threat to the survival of newly-described species. They monitor the scientific literature for new species descriptions, which essentially tell them exactly where to pick up the loot and what it looks like!
That at least is the message of a new podcast from the BBC documentary series One Planet, titled "The New Species Dilemma" (mp3 download). New podcasts are available for 30 days after broadcast.
In some cases, though, scientists are aware of this problem. When the famous Wollemi Pine (which even has its own official website) was discovered in Australia, its location was not made publicly known, and I think that still is the case to this day.
At the same time, proper scientific description requires full documentation, and that includes geographical data. It's an unexpected problem, and I don't think something that most taxonomists have to think about. But if you're working on a particularly "charismatic" group of organisms (and standards for "charisma" vary; some people collect exotic frogs, for instance) it might be something worth giving some thought to!