Despite many competitors, Dropbox is the de facto standard for syncing files across one's own computers and sharing them with others. New features rolled out Monday extend Dropbox's reach substantially by making it possible to create a public, revokable link to any file or folder in a Dropbox sync folder. Previously, only items in a special Public folder could be shared, and the links couldn't be canceled; the item had to be moved out of the folder.
Dropbox also added Web-based previewing of linked files, which lets someone following a link view a browser-window-sized look at documents and images, play audio, and view video. Dropbox hasn't released a full list of what kinds documents are supported, but supported formats include H.264 video (the format supported in iOS), Photoshop files, Word documents, and most image formats.
If you're already a Dropbox user, the update was slipstreamed on Monday into the software you already use on the Desktop. The change isn't very noticeable. Select any file or folder (but only a single file or folder at a time), and Control-click or right-click the item. The Get Link menu item is new. Select it to create a shareable link. With the Public folder, Dropbox creates a link instantly; with this new approach of sharing anything, you must wait for files that are still being uploaded to Dropbox for the first time finish transferring before a link is created.
Once you select that menu item for a file or folder that's fully synced, Dropbox opens a page in your default Web browser with the link as the URL. You can then copy and share that URL. The gear menu lets you remove the link, disabling future access. Dropbox doesn't yet offer time-limited access to a URL, something available with the soon-to-be-discontinued iDisk from Apple, and with other file-sharing services. Dropbox sets a limit at 20GB of public transfers per day for customers with free accounts, and 200GB per day for paid individual and business account holders.
When someone other than the owner of the file or folder views a shared link, files may be previewed; Dropbox also makes files available for direct download or to be added to that viewer's Dropbox. If the viewer doesn't have a Dropbox account, the Add to My Dropbox button's resulting dialog has an option to create an account. (Dropbox has a free level of service for up to 2GB of storage, and charges $10 per month for 50GB and $20 per month for 100GB.)
You'll notice a particular advantage for previewing movies and listening to audio with Dropbox's new sharing approach. Audio and video are transcoded from the files in a Dropbox folder into a lower-fidelity or lower-resolution version that can be immediately played. This saves you from having to wait for the full audio or video to download in the browser window.
Folders are shown in a slightly different manner than files. Items in a shared folder may be previewed individually and downloaded from the preview window via a tiny link shown in the lower right-hand corner. But the folder can be copied as a whole only via the Add to My Dropbox link, encouraging people to create accounts who don't have them.
The Public folder remains in place at this writing, and you can still select Copy Public Link from the contextual menu to get an old-style direct link with no preview. The Photos folder is managed separately, and while you can create a link from the main folder, you cannot create links to individual files in the folder. Control-click a folder in the Photos folder, and you can select Copy Public Gallery Link, which provides an album-style view.
Dropbox's mobile apps were also updated. In iOS, the app appears identical, but a link icon is now available for any individual file; folders can't be shared in the current release. Tap the link icon, and you can select to copy or email the public URL. Dropbox hasn't optimized its preview for a mobile device, however.
The ability to share any item is a distinct advantage, making Dropbox more useful to its users by making it easier to share files without requiring recipients have an account or are logged in. However, requiring a round-trip to the Web is awkward, and Dropbox should work to provide better lightweight options directly on the PC or Mac.
[Glenn Fleishman is one of the writers of the Economist's Babbage blog and is a contributor to Macworld and TidBits.]