It's closed source and there are concerns about that. (You can't audit it for privacy, encryption quality or bugs.) But it seems to be the most effective sync tool out there at the moment. I am using it, though if anyone comes out with an equally good open source alternative I would switch.
I'd love an open source alternative. That does bug me about BTS. However, I have much more faith in BitTorrent to handle it well, where security is in their interest, than I do in a company like Dropbox. Of course, never trust a company, so I'd switch to something open in a heartbeat.
I loved BitTorrent Sync but it's so glitchy about syncing. I can't figure it out. Did you have any issues with it? I am using Mac (Mavericks) on both computers I was syncing. I only use BitTorrent Sync / DropBox for moving items from my work computer to my laptop and I need to know that if I drop a folder in there at 5pm when I'm racing to class, it'll be there when I get home. After about 4 times of not having a needed file with me and having to remote in to make a tiny change or grab a PDF I created at work, I got sick of it. Dropbox never fails Google Drive is also now offering insane prices (15gb free, 100 GB $1.99, 1 TB $9.99, 10 TB $99.99, 20 TB $199.99, 30 TB $299.99) but if privacy is a concern Google may not be the best place. Also, there have been horror stories about people getting locked out of their accounts, etc. Always have your work, especially important stuff, doubled up. For big projects I often have a copy on my laptop, on my work computer, on the work server, and in my DropBox.
So far, I've had no problem with BT, and I'm blown away by how quickly everything synced for me. I migrated an entire terrabyte of movies and music through it and everything was there in less than an hour. I was always frustrated with dropbox for not working well with my phone, too, so Sync solved that problem immediately.
It's an unfortunate choice of name from a marketing point of view. Everytime I mention it to someone they react with "Whoa, bittorrent? Isn't that the illegal thing?" Ignorant, I know, but that's how people react. And when I mentioned it to a sysadmin he replied with "We would never allow bittorrent near our systems." I keep having to explain that bittorrent and bittorrent sync are different things.
It's the same thing with "whoa, torrenting? Isn't that illegal?" No it's an extremely effective way of spreading data through hosting elsewhere. Trying to explain to companies when they're worried about servers from heavy downloading, when I offer that they should make a magnet link they look at me like I've grown horns.
They should market the exact same service (because it's an awesome service) under two names for the two sets of audiences: the geeks (like me) who get off on this tech and the businesses (where the money is) who don't understand or care to understand. +$1m if they come up with a name containing 3 or more technology buzzwords and an acronym to go along with it.