Is NSA also spying on our documents on Dropbox?

Who knows? ALL of their activities are done behind CLOSED DOORS in SECRET sessions!

That said, ANYTHING you have "on the net" is available at any time to anyone who is looking for it. There is NO PRIVACY on the internet! Anyone who says different is LYING. Have you ever visited a site which no longer exists? How would you like to SEE what was there in the past? YOU CAN! Simply go to http://www.archive.org/ and type in the old URL. You will see a "map" of sorts showing you each and every time a web crawler visited the site and made a snapshot. You can click on a date ans SEE the site as it WAS on that date, even YEARS back in the past! The name for this is "the way back machine" in honor of the character of Mister Peabody on the Rocky and Bullwinkle cartoon show. Mister Peabody and Sherman would use a time machine, named "The Way Back", to visit past history so Sherman could see how the event really unfolded. So, take everything DOWN as soon as you can, but there is nothing you can do about the internet archive having a copy from times in the past. And then, start using a strong encryption program, such as Pretty Good Privacy (PGP) to encrypt your sensitive information. I have been encrypting using PGP for 20 years or so since 1993 or 1994 when my best friend since age 4 introduced me to PGP. MOST everything that I feel is sensitive has been encrypted since then, and THAT was BEFORE the way back existed. The way back has never seen MY unencrypted sensitive information. So, better late than never. You can't take back what currently is out there, but you CAN encrypt anything NEW so no one can get hold of it. Visit http://www.pgpi.org/ to download various versions of PGP. The last FREE version was 602i. While you are at it, get PGPDISK, a separate program that treats an encrypted FILE as if it were a disk drive. The file can be copied and such just as any other, but the contents are encrypted with a military grade encryption. I use PGPDISK files that are 1440K in size so they will fit on a 3-1/2" floppy. Yes, Virginia, I still DO use floppies for backups of my files! I also have a Sony Mavica digital camera which ALSO uses 3-1/2" floppies for image storage! My second Mavica used CD-R/RW disks for 200 mb of storage. I use these because the memory is totally non-volatile even if the battery dies... AND I can read the disk files in ANY computer with a floppy drive. I am not a Luddite, but I simply do NOT want to rely on volatile media... hence the floppies for anything critical and long term, which I also encrypt.

Probably..

If u have sensitive documents id move them to media like CD's or DVD's

You can download Dropbox for free here http://bit.ly/1zK8bCm.

The downside to having multiple computers is synchronization. Dropbox is the perfect solution for these situations.

There is a plethora of knowledge about ourselves all over the internet already