if the word is "word", I also enter --
ord
wrd
wod
So I add every permutation that excludes 1 letter.
Then I also look at the Qwerty keyboard and for "word" I'd enter the letters immediately to the left and right of the letters, --
qord
eord
wird
wprd
woed
wotd
wors
worf
Now if any of these combinations are actually words that mean something completely different, I don't enter it, so in no way is this misleading the visitor. It's just an attempt to capture a large portion of misspellings.
I've goosed our AdWords traffic by at least 10% using this, because the click-throughs are much higher for the misspellings since they can't find what they were looking for. I know it's not remotely rocket science, but it's a way to put to a simple algorithm how people misspell words. It's actually pretty predictable and takes only a little bit more time.
Not on my pages
Why not in alt="" of spacers and/or small graphical images where mouseovers are very limited.
Just because someone type in "wod" doesn't mean they don't want "word" -- how many of these are or are not your most profitably customers. Cheap people are not the only ones that mis-spell online.
Added... not all content posted is written by professionals. There are more mis-spelled words in web pages than people that mis-spell at search engines.
It's a little like the accidental tourist "beecause thheir ccarr brroke downn. And the city says... "not in my town... get out, your not good for business".