Those applications that were loaded originally from a dmg file, such as Firefox, probably would be OK.
But those that require full-blown installers, especially complicated apps such as Photoshop, would be missing important pieces, some of which might be in the system folder's folders, and invisible.
Some of the apps that install with the system so you wouldn't know which install method they'd use, could cause problems. For any of those, it would be better to use the free Pacifist, available at versiontracker.com and macupdate.com.
Pacifist reads the Apple install disk and reinstalls any app from there that you might need — minus, of course, any Software Updates that might have been performed on it.
Run a Mac-Forums search for Pacifist for more info on it.