I've been an avid Evernote user since the beginning (one of the first few thousand users). I use it to record all sorts of ideas, thoughts, notes, reminders, research, and references.
One year ago, my girlfriend was using Evernote (on my suggestion) to write her travel journal on our trip to Southeast Asia. I saw her note sync a bunch of times (the iOS app shows a little blue arrow when it's uploading). But one day she opened it and the note was gone. I contacted support but they couldn't do anything. (They offered her a year of free Premium service and "apologized for the inconvenience".)
Since then, I've stopped recommending it to people because I don't want to feel personally responsible if they lose notes too. I also have a tinge of doubt every time I record important information. My biggest worry is Evernote quietly losing a note, because once I record something in Evernote I typically push it from my internal memory.
On top of that, their iOS app is incredibly slow. When I want to quickly jot an idea down, it's very inconvenient.
I've started using SimpleNote lately, which is far faster, but I don't know to what extent I should trust it to keep my data safely.