I only upgrade my Ipod when I lose mine
. That happens a lot though
So, it's normally every two years.
Anyway, yeah, here's my history of Ipods.
2004: 4G 20GB Classic-I had only, like, 100 songs on it at the time, though
2006: 1G 1GB Nano-Don't laugh, I still wasn't really "into music" at the time, so the size was just right
2008: 3G 8GB Nano-My all-time favorite Ipod
2009: 6G 80GB Classic-Just got it last week