Unsure why people are moved to throw their data into the hands of someone (company) that would never treat their data sacred. I don't care what argument you put forth, no one is going to care (security wise) about your data as vigilant as you would (and should). Math wise, the cloud makes no sense to me, even on the free model.
1) wait for you to download your data over the Interwebs (mobile you say... tick tock)
2) There is NO GUARANTEE someone in the company isn't looking at your data or selling it. You're simply trusting they won't
Storage is dirt cheap. 2TB drives are like what 100-200 US per pop give or take. They're compact enough to throw in a messenger bag along with a laptop. Data availability is much faster than downloading it over the wire. Throw on crypto (say Truecrypt) and you have a decent amount of security. Only concern, is your HD goes bad. In either event, another backup 2TB is 100-200. Cloud pay for play? @ 10.00 per month, its STILL the cost if not more than buying your own device.