I have been using btsync for a while now and it works very well. But it is closed source software, which means you don't really know how well it protects your freedom or privacy. Sure, there's no central server, but do you know how the folder secrets are generated and that the code is not somehow backdoored? We really don't know. I hear that OwnCloud, which is open source, can do something similar, but I haven't tried it yet so I don't know how well it works.
Yeah, I suppose it's more accurate to say that the BT technology is open and trusted. I'm operating under the assumption that btsync is using the same. I do have questions about its supposed encryption though. I've started using it to sync my photos from my phone to my desktop though; something I was relying on Dropbox for previously.