From a blog I read:
"I hear lots of people complaining about the economy and how it’s effecting them."
I hear lots of spelling whizzes complaining about how the spelling is "affecting," not "effecting," them.
Most of the time, "affect" is used as a verb. "Effect," as in "the cause and effect of something," is usually used as a noun. Check the dictionary if you're not sure which one is right for your particular sentence.