I have a friend who literally didn't even scrape food off his pan when we was done cooking - just let it cool and put it away. When he took it out weeks later, it was green and fuzzy, and he just cranked up the heat until it smoked, and then scraped it clean. That's more than a bit extreme for me, but perhaps an example of how rugged it is.
I also really like my De Buyer high carbon steel skillet, but if I leave it out for 15 minutes without thoroughly drying it, it starts turning orange from rust. It's a bit finicky for me now that I've come to love my cast iron.