For goodness sake, K800i is a brick compared to the K810i.
The camera lens cover is also more prone to wobble in its place.
The keypad is made of rubberized plastic. After few months of heavy smsing, it will peel off.

K810i on the other hand is a fingerprint magnet.
The round metallic buttons aren't as bad as said. It's small and responsive. It's just that the width of the phone is wide, like the K800i, which makes it harder for smaller hands.