URL shortening services
URL shortening services such as shorl have been around for quite a while. They are very useful on places like twitter, IM, chat, etc. However, there is also an inherent risk with them. Once a URL is shorlified, you will not be able to tell where it will lead you to until you click on it. I have not seen any abuse of them, but it seems like an interesting avenue to pursue. Set up a drive-by site and create a nice shorlified URL (or even a whole bunch of them).