Ubuntu doesn't quite do everything a mac or PC does. You have to use emulators etc and the free ones like wine, really aren't very good. Its also more difficult to get the drivers for things like wireless cards, webcams and other such things. If you're going to install ubuntu, don't get rid of OS X totally, have your computer dual boot between the two. Since its an intel mac though, you could always just have it dual boot windows/OS X and then theres no need for Linux (which can be messy and difficult to use)!