i think 8 days is plenty of time. in fact for most people, it HAS to be enough time... i find it shocking that a lot of you are posting that you are able to travel to WDW for weeks or even a month at a time.
I don't know where a lot of you work, but i only get 1 week off at a time! so we have to make our trips work in a 7 day time frame.
we do each park for one day, then go back and do anything else we want again or hit up a water park or downtown disney in our free time... plus we usually find a way to end each of our nights in the magic kingdom... i don't know, i think if you plan well, you can hit everything you want to see and do.