Since I don't have much video on my iPod, I though 30 GB would be plenty of room. Our family music library used about 14GB, and a few videos used 3-4 GB.
I didn't reckon with Podcasts. I'm out of room now.
Ironically, this actually negates one of the relative disadvantages of my iPhone-to-be. I'm going to have be selective about what I carry, whether I use an iPod or a 16 GB iPhone.
If 30GB isn't enough, then 60 won't be either, so there's no point in trying to outpace this stuff. I just need to get used to managing the playlist sync.