Sure, it's comparatively trivial to share your files with others on Dropbox. But how do people know why you've shared a file, or what they'll get when they open it? That's what the company's newly introduced comment system aims to solve. You can now start a conversation around any shared file, so your friends will know the context behind that photo upload without having to ask. You can also invite anyone into the fray with a Twitter-like @ mention (whether or not they use Dropbox), and you'll get automatic notifications that let you know when an office pal has an idea for that group presentation. Comments are only available on the web right now, but they should be accessible from mobile apps "soon."