Apparently it was too expensive for Dropbox to run public folders:

Why did Dropbox feel the need to [end-of-life public folders]? The official reason is a decidedly pragmatic one. According to their email, the new link-oriented sharing model is a more scalable way to handle the sorts of use-cases that people use the Public folder for, which is sure to help as the service continues to grow (they tiptoed over the 50 million registered user mark a few months back).

The move to all-private-except-things-with-obscure-links moves Dropbox one step closer to a collision course with Evernote.

Both are services that let you access all your (private) stuff from any device.

It's going to be interesting to see how this all plays out. They now iCloud and Google competing against them. It's easier for them to get minimized if they are not at the forefront. There's other smaller players like cubby trying to get into the market as well.

Yes, because Dropbox and Evernote proved how lucrative their markets are, they're likely to get a lot more competition.

Dropbox more than Evernote at first, but I still think those two companies are on a collision course.

The move to all-private-except-things-with-obscure-links moves Dropbox one step closer to a collision course with Evernote.

That will be very interesting to watch!