zoneking - if you have an All Zones travelcard, you would have none of those fears. If you would like to learn more about the intricacies of Oyster, you could attend one of our fares workshops (or meals) and we'll be happy to explain any queries you have, and give you tips on how to ensure that you don't have any problems (or, if you do, how to manage it and resolve the situation).
I used to be anti-Oyster, back when it was LU only and a lot of the facilities that are now available, weren't back then, but I'm definitely converted now! (I am sure MetDriver will remember that!)
blindtraveler - as far as I am aware, Travelcards are only available in 1 day (paper only), or 7 day, or any period between 1 calendar month & annual. There is no option, as far as I am aware, to purchase a 2-day or 3-day Travelcard (unless there are some arrangements specifically for tourists sold through Travel Agents, or similar)