[Groxx]

Important point:

Any file or folder in your Dropbox is now linkable!

But not quite yet, presumably very soon. Apparently appears in the 0.8 beta clients only, didn't see anything specific about the website (though I don't see it on my account).

[edanm]

Another important point (mentioned in a later comment): unlike public folders, only things you choose to make linkable can be viewed. The public folder continues to work the same way.

[malbiniak]

If you're feeling bold, here's a link to the experimental build:

http://forums.dropbox.com/topic.php?id=21406&replies=22