I bought an ITouch a few weeks ago. I downloaded that app too. Isn't it cool. I like how you can combine blocks and change the colors. It is a nice tool.
Be careful though there are alot of apps out there that are useless. I downloaded one that has 3 screens, one tells you how to do a setting triangle, one gives you bed sizes and the other is actually a piece of fabric with different lengths of stitches all equaling an inch with a pin on either side of the inch mark. I'm like, and the point of this app is what exactly?
Robert Kauffman has one where you can calculate backing fabric and a bunch of other stuff.
I like the Fabric Stash one. You can take a picture with your ITouch or Iphone of your fabric and enter it into your database with an inventory of how much, so when you go to the store you know what you already have. I buy duplicate fabric all the time thinking I don't have it.