When upgrading from Snow Leopard to Lion, there is a chance of compatibility issues between app and the new OS. A new site called RoaringApps comes to the rescue by displaying what apps are compatible with the new OS. RoaringApps provides a long table of apps showing what apps are supported and if it is available in the App Store.
Other parts of the site include a forum and IRC chat to talk apps. This makes a great way to assure that all of your Mac applications are going to work, before you upgrade.