I use them every time I go to WDW!
My advice is to get them in fairly large denominations (I get most of mine in $50 denominations). Because we stay at Shades of Green, we can't use the dining plan or charge things to our room. I use travelers checks for things like all my meals, snacks and souvenirs, and usually bring about $600 worth.
If you choose large denominations, you don't have to get nearly as many travelers checks. My first trip, I got them mostly in $20s, and it was a pain to keep cashing them all day long. Plus, because of the sheer number that you have, they get bulky in your wallet if you get smaller denominations. When I get them in $50s, I can cash one or two per day, as needed, and use the change (which is in cash) throughout the day.