btsync is really nice, just install the software, no account creation needed, and if you just want to sync computers on a LAN, no internet connection needed. I was worried about btsync being closed source but when I looked at alternatives like dropbox and spideroak I noticed they weren't open either and you have to sign up for an account and give them personal information to get serious amounts of storage.
Everyone who's looking to run their own private Dropbox should check out ownCloud[1]. It's free, open source, you install it on your own server (or Raspberry Pi), and it's not P2P like BTsync is. It works more like Dropbox, with a centralized server. You just run that server yourself.
They have apps for Windows, Mac, Linux, iOS and Android. I've been using it for about two months now with no problems.
OwnCloud is quite nice, but its Dropbox-like feature isn't his best asset. We have big shared folders and the client app does weird stuff sometimes (and given the way things are architected, I'm not confident it will change).
On the other hand, it gives you a nice web-based file browser, CardDav, CalDav, and a RSS webapp. And there's a basic iPhone app.
The approach posted somewhere else in the comments[0] seems interesting. Use BTSync for the synchronization, and put ownCloud over that for the web interface and other goodies. I'm tempted to experiment with that.
I used ownCloud for both the CardDav/CalDav/etc. and the dropbox-like stuff for a couple of months now. Sadly as you say the dropbox functionality doesn't work well. It takes up to several days until every file is synchronized everywhere and I want to synchronize almost my whole /home directory between my ThinkPad and my iMac.
A couple of days ago I installed btsync and tested syncing one 130 MB big directory. I added it both at the same time to btsync and ownCloud. After about 2 minutes btsync had its copy on the other computer. After one hour ownCloud had cpied about 50 MB to the server when I canceled it and removed the ownCloud dropbox-client from my computers.
I still use all the other stuff to synchronize my calendar/address book between my computers and mobile devises and I even use their RSS backend but with my own Firefox OS app https://marketplace.firefox.com/app/feedmonkey/
The CardDav and CalDav stuff was a hassle for me to make work. After the trial and error and googling, getting it set up myself, I pretty much had to grab each family member's mobile device or computer and punch in the magic codes. But once I had it going... It works! All of our calendar and contact data is available on each of our computers and we can share them easily.
Even if it's nice, I won't recommend it to anyone. If it becomes big, I don't want the next Edward Snowden to tell me it's been used by .gov in the future.
