Right now, it's only on the iOS platform, so anyone with an iPhone or an iPod touch can leave a tip on any topic they can think of. There's no way to verify the source of the tip as of yet (unless the person explicitly states it in the tip). The identity of the author, however, is tied to their Facebook (and later on, Twitter) account.
If it takes off, we have plans to expand to the iPad and the Mac platforms, and then possibly a web and an Android version.
