The official uninstall instructions for Evernote on a Mac are incomplete. They just say “trash the Application”. But that leaves behind a launchd entry that every 10 seconds tries to launch EvernoteHelper, now missing, and spams the syslog and creates lots of useless crash reports.
Anyway, the fix is to run
launchctl remove com.evernote.EvernoteHelper as the user you installed Evernote as. (Not root!)
launchctl/launchd is a total mystery to me. It seems awfully complicated. “launchctl list” and “launchctl bstree” are helpful commands for inspecting the state of what’s trying to launch.