Never. I even do diphthongs (oesophagus, encyclopaedia etc) , include the "u" in words like honour, colour and humour, the second "i" in aluminium, shun "zeds" in words like realise etc. I can even spell manoeuvre (and watch all the American heads explode).
I never misspell words, my computer does. The keyboards are not ergonomic and the characters are printed in gray on black keys (on some keys the print is worn away completely). And often, I'm wearing the wrong glasses for reading the screen. Fortunately, the computer also lets me know if something is misspelled.