I think I've got one world where I did a fair bit of deep mining and got a decent amount of iron (even after building armour and buckets and stuff) - when I found out that depth actually made a difference, so I actually dug down deep - but I wasn't fond of the location of that one, so I gave up on it.
Other than that I've been mainly building/sculpting basic things, and not yet got around to doing more mines below sea-level to actually get the rarer ores.