What kind of data are you protecting, and how badly does someone else want it?
Unpublished novel drafts: probably worthless unless you are J. K. Rowling or Neil Gaiman.
Personal correspondence: financially worthless, possibly extremely embarrassing if it falls into the hands of someone with a grudge against you personally, or you are a politician or other public figure.
Financial and medical information: Again, unless someone has a grudge against you personally, this kind of data is valuable only in bulk. That’s why the bad guys spend their energy breaking into Target and Blue Cross.
Account-specific banking information: How much money is in your account? The more valuable the account, the dumber it is to put the information on any publicly accessible server anywhere.
High value corporate or national security information: Here, all bets are off. You’re trying to protect the data from people with way more resources and motivation than you have. Nowhere on the internet is safe. Few physical locations are safe. Seek professional help.
If there is a specific reason for a specific person or organization to target you, personally, then you should be very very paranoid. Depending on the amount of resources and motivation you’re up against, there’s a good change that you’re going to lose your data unless you are, or hire, a security professional.
For the rest of us, protecting low value information from random people on the internet? Meh. There are bigger, more attractive targets out there.
With that said, no way no how am I putting my banking passwords anywhere that I don’t hold the encryption keys. And I use two-factor authentication for every service that supports it, including Dropbox. But putting my work in progress in Dropbox? No worries.