If one of our peers can make the mistake, then they must indeed be rather difficult to distinguish, so let's analyse them.
In the first instance, both affect and effect have their verb and their noun forms, but it's safe to mention here that affect as a verb is more common than effect the verb, and, likewise, effect as a noun is heard more often than affect as a noun.
affect, verb /əˈfekt/
If something affects someone or something else, it changes or influences them.
How will the new cutbacks affect us?
Even the threat of rain does not affect his decision to go for a run.
It is often used to talk about causing physical damages.
Northern Japan was badly affected by the enormous seaquake and tsunami.
How badly has New Zealand been affected by the recent oil spill?
We also used it to refer to strong feelings or emotions.
The kids have been deeply affected by their father's death.
There is no telling how their parents' divorce will affect them.
effect, verb /ɪˈfekt/
This is a formal verb and isn't used much. It means to achieve, to produce, to make something occur.
Seeing how badly their divorce has affected their children, they are trying to effect a reconciliation.
affect, noun /ˈæfekt/ (Notice how the pronunciation differs from that of the verb)
This is even rarer than effect as a verb, and is most often used in psychology and psychiatry to refer to feelings or emotions. We are more likely to hear affection /əˈfekʃ(ə)n/, which refers to a feeling of caring about someone or something.
effect, noun /ɪˈfekt/
This is used to refer to a result or an influence.
They are studying what effects the oil spill has on the ecosystems around the area.
Do you think technology has adverse effects on us?
For more meanings on affect and effect, consult a good dictionary.