I got the base 15 inch 2010 model with the 320 GB harddrive. I plan to use it for college and movies/music/pictures. I have had it for two months now and have already used up 150 GB. Is it worth it to upgrade to a bigger internal drive? or should i buy a 500 GB external drive instead? if i do buy a bigger internal drive, i would have to buy an even bigger external for backups. Thanks for any suggestions/experiences.