Appsolete is a nice system utility that can help in your switch to OS X Lion. As you may have heard, Lion no longer supports PowerPC apps. These were supported all the way up to Snow Leopard to maintain support for PowerPC based Macs. When you make the switch to Lion, you will find that PPC apps will no longer run. Appsolete can scan your applications before you make the switch, or even after, and tell you which applications on your Mac are not going to run when you install Lion. If you have a lot of applications, you will appreciate the time that you can save by carrying out a simple scan with this tool.
When you launch the app, it will scan not only your Applications folder, but your entire Mac for apps that are no longer supported, and it will list all of them. You can click on an application on the list and show it in finder so you can either delete it, back it up, or do whatever you want with it. From the application, you can search for updates for the selected application, which will launch a browser tab headed to a search on MacUpdate. If there are updates available, you can download them and carry on.
Appsolete displays some information about the apps that are obsolete. It tells you where they are located in your Mac, when they were last opened and what their version number is.
In a nutshell, Appsolete is one of those apps that are perfect because they are simple and very functional. The only thing that I would add is a way to scan a specific directory instead of your entire Mac.