Dropbox policy says you must not use the service to:

+ publish or share materials that are unlawfully pornographic or indecent, or that advocate bigotry, religious, racial or ethnic hatred;

+ violate the law in any way, or to violate the privacy of others, or to defame others.

https://www.dropbox.com/acceptable_use

Apple says you can't use their service to:

a. upload, download, post, email, transmit, store or otherwise make available any Content that is unlawful, harassing, threatening, harmful, tortious, defamatory, libelous, abusive, violent, obscene, vulgar, invasive of another’s privacy, hateful, racially or ethnically offensive, or otherwise objectionable;

http://www.apple.com/legal/icloud/en/terms.html

Google doesn't seem to mention content beyond the DMCA (maybe I'm missing something):

We respond to notices of alleged copyright infringement and terminate accounts of repeat infringers according to the process set out in the U.S. Digital Millennium Copyright Act.

http://www.google.com/policies/terms/

All those only trigger if you share your files publicly. That's fine, but what I don't want is a cloud provider looking through and judging files that I don't choose to share with others.

Perhaps there is context missing but the Apple one above refers to "uploading" and "storing". Seems like it would apply to anything you put in iCloud? And since it includes the catch-all "otherwise objectionable" it would seem to make it quite open ended, almost unusable really.

But the thing is that they are (probably) not actively scanning your files for such content and those terms only come into effect if you're reported by someone.

Plus "unlawfully pornographic" is a huge different to "any kind of partial nudity".