I use evernote for keeping notes on various topics (it has other functions which I haven't used). I recently paid for a yearly subscription and regret doing so. I always seem to be getting duplicate notes appearing after having updated them, or get 'conflicting modification' where my notes within a section are duplicated but with some minor differences in one version (whatever you edited). Trying to spot the difference and resolving this is far from straight forward and I've wasted a lot of time doing so. I'll be transferring my notes over to google docs in future (much more reliable) and won't renew my subscription.
