The short answer is yes, you can use your room card or charge card for everything at WDW.
But here's what we're doing:
We'll be on the Dining Plan this next trip and because of that we've decided not to put charging privileges on our room keys. This way when we use our keys to "pay" for our meals with DDP points there will be no confusion. On our last trip there was at least one time that the server charged our meal to the room instead of against our DDP. We've also read others on the board have had an issue with this from time to time. So we'll just use our regular charge card if we want to charge something. Just thought I'd mention it.
on souvenirs/boat rentals/bike rentals, etc. during our 9 or 10 day trip. 
We're actually using Disney Gift Cards. The kids each get their own for their spending money and then DH and I will have one for everything else. You can reload it in the parks if you run out. That way, I know exactly how much we've spent, so no big surprises at check out (well, we're also staying at SOG, so no room charges..but I'd have one heck of a Visa Bill!!! I plan on carrying a small amount of cash on me, just in case, but everything else either the Gift Card or my Disney Rewards card. We don't have the dining plan, so those 2 cards will see plenty of action!
I was really glad to see this post because we had discussed doing this, but the clerk at the Disney store here in Pittsburgh told us we could not use the gift cards in the parks. We thought it would be better if the grandchildren each had a gift card so they would be more aware of what they were spending. They have all saved for this trip but I know they will forget where the money went if they just have cash. I had planned on some cash for each day and a gift card for souveniers and things so this will work out great
http://disney.go.com/disneygiftcard/faq.html
Here's a link to the Disney Gift Card FAQs. I bought mine from the Disneyland Resort Website. I opted for them because they have several different designs...That way, each child gets their own so I can tell them apart. It's free shipping on the cards and you can get them for $25, $50, $100..If you want to add more to it, then ou can take it into a Disney Store or at WDW..You can also buy them at a Disney Store.
