I'll second this as well - I don't want to turn off auto-correct, but right now it is WAY too aggressive in Evernote. As other posters have said, it is far easier to reject corrections in other applications, where in Evernote it is very difficult. I've resorted to typing the sentence, then going back to fix errors, being careful not to press the spacebar which will trigger a re-"correction".
Here's a very concrete example:
Type this: Tukey
Press the spacebar, and Evernote "corrects" to "Turkey"
Backspace over the r, leaving just "Tu" and type "key"
Press the spacebar
In Evernote, "Tukey" is again replaced by "Turkey". No matter now many times I take the above correction step, Evernote is steadfast that I'm wrong and it is right. In Mail, which in theory uses the same Mac-wide autocorrect engine, "Tukey" is left and is underlined in red after my correction, which is the correct behavior
So, please don't add a special "disable spelling" for Evernote, just make it behave well as it does in other apps. This is just a bug that needs to be fixed.