I've been using it for a while now, and am very happy with it. Every change you make inside the specified folder is replicated straight away - which can include undesired changes or deletion - but you can undo any changes on the website. There's also an iPhone / iPod Touch app, which gives you access to the files and lets you store some for offline reading.
If you want to try it, I have a referral link you can use,
here; this means we both get a little extra space, over the standard free 2GB.