The latest version, 1.0.116, adds a few new features like one-way and one-time syncing as well as the ability to exclude specific files or subdirectories from syncing.
After spending a few hours today syncing various files across different Windows and Mac devices, I was mostly impressed by BitTorrent Sync. The installed application is lightweight and the interface, straightforward and logical. Transfer speeds were blazing fast, and the syncing system seems to be both easy to use and secure. Each "Shared Folder" in BitTorrent Sync receives a 32-character key (randomly generated or user designated) that must be entered on another device in order to share. All of the traffic shared between devices is encrypted with Advanced Encryption Standard (AES) using a 256-bit key based on your 32-character "secret." Along with the new "Read-Only" setting for folders, the latest versions of BitTorrent Sync allow for a one-time file transfer, using a key that expires after a certain amount of time (24 hours is the given estimate.)
For me, files have synced very rapidly so far (likely because of our robust corporate network), and the Transfers and History windows provide useful, if limited, information about the shared files within the shared folders. Running BitTorrent Sync on Linux and NAS devices may not be as simple as the native Windows and Mac clients, but Sync also has a WebUI available at YourIP:8888/gui (where 8888 is the default port that can be customized) as well as a Command-Line interface that will provide a list of available commands when given the standard "--help" argument.
With BitTorrent Sync, because you are syncing files between two or more "devices" (there are no mobile clients yet, though support is expected in the future), there's no Web site like Dropbox.com to access your files from an unsynced computer or phone. However, for the pure task of seamlessly syncing specific files or folders between multiple computers, BitTorrent Sync worked great. Despite the project's alpha status, BitTorrent Sync has instantly become a significant player in the file-transfer and syncing app market.