If you don't know the difference between affect and effect, learn it

I think it's more common to get this one wrong than to get it right, even though it's simple.   

Impact / affect:

 

Impact has traditionally been only a noun.  In recent years, however, it has undergone a semantic shift that has allowed it to act as a verb.  So uses such as the following have become widespread (and also widely condemned by stylists):  "The researchers concluded that this low level of intensity may have impacted [read affected] the results." (citation and other examples omitted)

 

This use of impact would be perfectly acceptable if impact were performing any function not as ably performed by affect or influence.  If affect as a verb is not sufficiently straightforward in context, then the careful writer might use "have an impact on," which, though longer, is probably better than the jarring impact of impacted.  Reserve impact for noun uses and impacted for wisdom teeth.

 

Interestingly, impact as a verb might have arisen partly in response to widespread diffidence about the spelling of affect.