free (beware of conflicting with your own keywords e.g. "risk free")
Please everyone, read that again.
If you offer a "keyword free trial", don't use the negative keyword free.
I think many people have gotten to the point where they have a huge list of negative keywords that go into every group without thinking about it, that they are actually conflicting with their keywords instead of making custom negative keywords lists based off the actual keywords in the group.
Many words can end in '...ise', or '...ize'. Invariably American-ised English will favour the latter.
Likewise, always remember the American tendancy to miss out vowels (in order to make words easier to spell ;-p); such as color & neighbor.
Medical terms as keywords: there is likely a variation in spelling on the others side of the pond.
My tuppence ha'penny's worth...
Syzygy
That is, if "Software Cracks" is a keyword listed by the tool and not "Software Crack", then I don't bother adding "crack" as a negative keyword. The singular version probably gets 2 impressions per month.
The time saved by not adding the singular version in the above case can probably be used for other productive work (like bid changes).
Spelling variations in the English language ...
And what does one do when the proper spelling of a place is "Something Harbour" instead of "Harbor" or "Quay" or "Cay" instead of "Key"?
I run into this problem all the time where competitors will spell the name incorrectly just to get hits from Americans unfamiliar with the "correct" spelling!
(I don't intend that last statement as a jab at how Americans spell, I am just pointing out that the correct spelling of the name of a place should not be tampered with.) :)