Advertising is how we support the development and delivery of the free version of Solitaire.
If you prefer to play our game without ads, we also offer a paid version of Solitaire for $4.99 with no advertising. You can download the paid version Solitaire here - http://itunes.apple.com/us/app/solitaire/id284791396?mt=8
If you do purchase it, a separate install of Solitaire with a gold border will be the paid version. The free version will not be overwritten or removed as it is a separate application.
Just note that if you do purchase it for $4.99, that the statistics are not be transferred over to the paid version as Apple treats every application independently, so you will start off fresh.