I travel around 2 hours to and from work, and have another 2 hours to listen to my iPod at work, meaning it'd be much too restrictive to only have room for 5-6 albums. I listen to a huge variety of different genres of music, from Classical to Gospel to Jazz to Blues to Rock, and everything in between, including audio books. Now that I'm a spoilt iPod owner, I don't think I could imagine first having to choose 5-6 genres, then choosing one album for each genre.
I don't get that much time at the computer anymore, so I love the luxury of being able to simply dump all of my audio books and music onto my iPod, and not need to plug it into my computer every time I finish one of my audio books, or feel like listening to something new.
I also have a whole bunch of TV episodes on my 80GB, including the complete series of Seinfeld, The Simpsons, Ali G and Family Guy. Again you could argue that I won't be able to watch them all in one sitting anyway, but I watch them during my daily workout, which means I get through around 5-6 episodes a day, and it'd be too much of a pain to have to replace the episodes that I've watched every day.