According to the folks at the Oxford English Corpus (a database of a billion words), there are some terms that are now misspelled more often than spelled correctly. Here are a few--see whether you're one of the guilty ones!
strait-laced (not straight-laced)
just deserts (not just desserts)
free rein (not free reign)
sleight of hand (not slight of hand)
fount of knowledge (not font)
fazed by (not phased by)
vocal cords (not vocal chords)
a shoo-in (not a shoe-in)
any more (not anymore)
some day (not someday)
under way (not underway)
I confess I've made a couple of these mistakes myself (somehow chords seems to go with vocal, doesn't it...).