Dear Mr. M:

You wrote:

>I think you should add an entry to the ‘Common Mistakes and Tricky Choices’
> page.
>
> One error that I encounter from other is the confusion of ‘effect’,
> ‘affect’.
>
> Effect is of course a noun, while affect is a verb.
>
> People are constantly getting these confused.
>

We have this in our Spelling Slammer software which comes with the deluxe versions of Grammar Slammer. It is a common problem, but we have considered it a spelling problem rather than a grammar problem, so we have included it in the spelling component of our software.