This afternoon among Apple's many upgrades and updates, the company announced a bunch of Apple branded features, that already existed via other non-Apple services. Apple has always liked the idea of keeping its loyal users within Apple-land as much as possible, so it's no surprise that many of the iOS 6 and Mountain Lion features do just that, offering an iVersion of an already existent product. As using Apple compatible stuff is much easier than not, we foresee near death or at least pain and suffering for these companies.
What it does: Dropbox was a cloud service before Apple iCloud. With Dropbox users can share and store files over the Internet, a.k.a in the cloud.
Why it's now obsolete: With Apple's fuller iCloud integration in Mountain Lion, users don't really need a separate cloud service, do they? Apple has had iCloud for awhile now, which works a lot like Dropbox. But the latest iCloud Documents upgrade will have the just-works elements of syncing Messages, Reminders, Notes, Pages, Numbers and Keynote.
Is it hurting already? Dropbox has seen this move coming for awhile, as Apple made the iCloud announcement a few months ago. So, Dropbox has been at work on features it thinks will keep people on the service. A few weeks ago, it began offering a sharing tool that lets people share with just a link, making the service ever-easier to use. It has also started concentrating on its non-iOS partnerships. Just today, Dropbox announced it now offers streaming video sharing in its Android app. A few months ago, it made a deal with HTC, offering phone buyers 25GB of free storage for two years.