well, depending on what you want to do, 1gb should be fine. if you give the os 500mb, that's still 500mb for media, way bigger than 64mb. and you'll still have almost limitless space for installing apps, which will take no space on the media partition. i find that reencoding videos makes them run much faster, and it comes out to about 50mb for 20 mins. easily fit a couple of movies in 500mb.