Yeah, I've noticed this too - and think it's quite worrying. The 800 isn't holding value well at all, and that means there are a lot on sale, which in turn means people aren't keeping them when they choose them as contract upgrades.
In the UK, I've seen auctions go for less than ?250. That's very low. iPhone 3GS low. Despite all the positive news of how many Nokia have sold, it doesn't mean much if they're being sold on presumably because people don't like them/Windows Phone.