Seriously, I'm seeing the word "definitely" now spelled more often incorrectly than correctly. I think that's no exaggeration. Usually, it "definately," although I've seen many variations. That includes completely getting the words "definitely" and "defiantly" mixed up.
I just found this--
Not definately. Not definatly. Not definantly. Not definetly. Not definently. And certainly not defiantly. The correct spelling is definitely.
And this from the Urban Dictionary--
Definately
Idiot-speak for "definitely". One of the most common moronic misspellings found on the internet