I have a 160 gb right now, in a couple of weeks im putting the 160 gb in my pc and putting the one in my PC (80gb) in my xbox.. this is because I barely use any of it and i'm not sure if anyone else does this but.. if you beat a game or get bored of it, why dont you just ftp the game to your pc and save it to a folder, make sure you dont delete it... so you can store all your games that you don't play, or beat on your PC.. if there's ever a time that you want to play the game that you stored on your pc, just ftp it back to your xbox! (i'm sure a lot of people do this). My suggestion to people browsing this topic that are not sure of what size HDD to get, it's simple. If you have a lot of music, vdeos, or pictures, and of corse, games, and whatever else, get a large HDD (120-300gb). Or if you just want your games on the HDD i reccomend getting between 60-100gb, and do my method to store the games on your pc.. I forgot to mention, just to make sure that the games you have stored on you PC are safe, you can burn them to a cd-r!!
Good Luck!