Also, I'd mentioned a recent pair of TechRepublic.com articles on attacking (encrypted) DropBox files. I don't have their links but have my saved copies of their articles (attached - I hope this attribution is sufficient not to violate their copyright). In summary, though, do NOT rely on cloud's encryption but encrypt before uploading (if that's how you want to save your files).
Thanks, Wyatt, good information about the iPhone. Do you know if Androids do the same? Any recommended app?