I really wanted to like Ubuntu One, but like others I have experienced problems with the sync function. I upgraded to Ubuntu 11.04 recently and hoped Ubuntu One might have better functionality, but it didn't happen. I ended up giving Dropbox a chance and it works great. Installation was easy on my Ubuntu and Windows machines. The best part about it is that it syncs perfectly! I would drop stuff in the Ubuntu One folder and the files would fail to upload. Now I drop files in the Dropbox folder and they upload without issue. I ended up removing Ubuntu One from my system. I plan on trying it again in the future though, but for now Dropbox certainly has the advantage over Ubuntu One.