I remember the day a year and a half ago when I went out apartment hunting in a new town, looking at my notes on apartments in Evernote's Android app. It was a complex note, with lots of text in deep hierarchies of bullet points. At one point I tried to edit it, and after a few visual glitches, the text of the note disappeared. Then it synced, and there was no undo or history option in the app as far as I could tell.
I was able to get the note back by driving back to my hotel, retrieving my laptop where the note was cached, and opening Evernote while offline to ensure it wouldn't sync and wipe out that copy. Pretty frustrating. I've learned some tough lessons about cloud services and free stuff.