Comment Re: Cloud != Backup (Score 2) 310
There are two aspects to data security. The first is can anybody else gain access to make a copy. The NSA probably has backdoor access to Dropbox, as anybody who can guess your username and password (just like an open ssh server). So having a strong unique password is important (just like for your email account). Anything really important (like my bitcoin wallet) is encrypted locally with a strong password before being mirrored to Dropbox, but otherwise I don't believe the NSA would be a threat to my personal safety even if they did know the contents of my filesystem.
Dropbox acts as a real-time offsite backup. The security here is that if I lose my laptop (and local backup disks), then worst case I can simply buy a new laptop, download all my personal documents from Dropbox and start working again on the same file I was working on just before my laptop disappeared, with minimal lost work assuming I am connected to the internet (a local backup will miss all work since the last backup). Its worth having an occasional local backup solution as well, such as an Apple Time Machine, as a backup for the backup.
Dropbox also guards against file corruption. Usually this takes the form of "opps, I didn't mean to delete/overwrite that file". These will usually occur to files I am actively working on and the previous desired version of the file may have been written only minutes/hours ago. This includes programming files that have got yet been committed to version control. A daily backup won't help here, but Dropbox will (I just need to login to the website and click undelete or previous version).
So in short, Dropbox is a very convenient real-time offsite backup that can protect against both catastrophic data loss and individual file corruption. It even doubles as a basic automatic version control system for your filesystem. The bet is that that I won't lose my laptop at the same time the Dropbox servers suffer catastrophic data loss as I can always reupload my data if Dropbox loses all its data. The security risk is that you are potentially exposing your data to Dropbox, the NSA and anybody who can successfully guess your username/password.