I run Ubuntu on my Samsung ARM
I gave Ubuntu One a month. To be honest, I don't like it very much. There's no taskbar status icon (there is a third party one, but I couldn't find a binary for ARM processors). It does give status updates in the corner of the screen, but they were super-annoying and sometimes they would stay in front of my windows until I clicked on them. I could live with those problems, but even though I haven't had any activity in my synced folder Ubuntu One on my Windows PC was constantly syncing, or at least trying to. I restarted the program and restarted my computer, but it kept having trouble.
So I looked around to see if there was an updated version of Grive. There was, but no ppas had it for ARM. I did see a Dropbox Bash script which seems really cool, but it seems to upload or download only, no two-way sync.
Long story short, I stumbled upon BitTorrent Sync, which is closed source but still has a PPA, with an ARM build. I was a little worried that it would be hard to set up. Not at all. It was super easy, working within minutes. The hardest part was copying the key from one PC to another in order to share the folder across them. It's only configured to work over my home network right now, but I think you can set up a tracker so you can sync the files over the internet.
-I wish it were open source, but to be honest I'd be happy with a closed source Dropbox or Google Drive client if it were offered by their respective companies, so I can get over it. I do think the technology could have far wider aspects if it were opened up, for instance artists giving out read only secrets to their people to download a video/album, and unlike a torrent file (afaik) they could change and update the files to fix errors without needing to give everyone a new link/key/secret.
-I don't understand the security. There's no username or password, just a "secret" that is tied to your folder. It's very unlikely that someone else has your secret, especially if it's generated by BT Sync itself. Since I'm only using it over wifi in my home network I'm not too worried about that.
-I've seriously beefed up my backup systems as a result of using BT Sync, until I can see how well it handles things. The biggest problem is by netbook stops in it's tracks as soon as the screen times out or I shut the lid. That is good for battery life, but bad for syncing, because BT Sync can only sync to another device, not a central server. As a result I've pulled out my old cell phone, set it up to never sleep and have the BT Sync client constantly on so it will always be there to update things if my phone-phone or my gaming laptop are asleep. My old phone also has FolderSync (an Android app I highly recommend) sending my working folder to Google Drive in---get this---a timestamped folder. I looked all over for an app that could zip a folder with a timestamp automatically and put it in folder synced with Drive. Then I discovered FolderSync could send it, not zipped, but timestamped at least, so it stays unique and left alone bu future uploads. This is in addition to local backups on all my computers and their own cloud syncing setups.
In short, it had a ridiculously easy setup. It's working very well so far. I wish the mobile app would tell me which devices it's connected to instead of only telling me the number of devices. And I do wish it were open source. I'll rate it 5 out of 5, with the provision of dropping that to 0 out of 5 if the security is proven to be absolute shit.