If you use any of Unsanity's haxies make absolutely sure you uninstall the APE manager before upgrading the Tiger install. This caused huge issues for people when Leopard came out. Also, take note that ShapeShifter doesn't work in Leopard.
What MacHamster said about the iLife thing.
Basically, just go through your Apps folder and anything you're unsure about throw into a Google search and you'll have your answer, as there's no way for us to give you a full-scale "Yes" or "No", especially when the contents of your Apps folder is a mystery to us. Generally speaking I've never had an issue when going from one system to the next, but everyone's mileage varies.