Don't worry about it. the sizes are minimal. 60GB (assuming you are getting premium) is plenty. I have about 4 game demos, Tekken DR, movie trailers, a couple of virtual PS2 mem cards on the HD and I still have 45GB free.
I also have a 2GB SD card and a 2 GB memory stick in it, unused except to back up my saved games (they are sometimes used to move photos and video files though).