I've had my mother on Aricept (10mg) for around 3 months now....the results, or lack of, are still unclear as of yet. It'll probably end up being one of those scenarios where we'll never know if it does/did any good or not, since there isn't anything out there than can reverse Alzheimers.
Do take note of my #4; it's possible that a year or two from now you will be very glad of knowing it!