This error is starting to have an effect on Mr. Rewrite. It's just too easy plug mistakes such as have an affect, has an affect, having an affect, had an affect into Google News and come back with scores of affect/effect errors by those paid to know better.
It's the same story with the affect, affect change, no affect and any affect, all errors (yes, affect can be a noun -- generally considered obsolete -- meaning a disposition, feeling or tendency, but grant Mr. Rewrite some latitude here).
So concerned is he that Mr. Rewrite will wade in on a point of grammar and risk death by a thousand nits picked by cyberstalking grammarians. Here we go, with a tip o' the virtual cap to the Blue Book of Grammar and Punctuation:
Effect applies when you're talking about bringing about or causing. An example: That mistake effected a bout of retching in Mr. Rewrite.
Effect applies in reference to a result. An example: What effect did the mistake have on Mr. Rewrite? He retched.
Noting Mr. Rewrite's parenthetical above, use effect when facing a choice after these words: a, an, any, the, take, into, no. Why? Just do it because Mr. Rewrite told you so. An example: Following Mr. Rewrite has had a chilling effect on my ability to communicate in English.
Affect applies in reference to influencing rather than causing. An example: How did the retching affect Mr. Rewrite's outlook?
Affect also is a noun meaning emotional expression, but this point is so fine that Mr. Rewrite would simply write around it rather than deal with this issue.
Valentine's Day didn't have the desired effect on Mr. Rewrite's Valentine's Day Apostrophe Confusion Watch (TM). Google News indexed a patriotic 1,776 botched references to Valentines Day, no apostrophe. Who knows? Maybe coverage of the big day will push us to Mr. Rewrite's goal of 2,000 misspellings.