If you have a lot of older programs hanging around on your Mac, chances are some of them may not work correctly (or at all) after upgrading to OS X Lion. Most programs put out in the last few years should at least launch in Lion, though it may be some time before they run well. However, there is a certain older class of application that won't even open anymore once you install OS X Lion: PowerPC-only apps. Before upgrading to Lion, it's important to know if you have any of these
