Actually a lot of this stuff will be added to Minecraft eventually
If I remember correctly, Notch said he was currently already working on a sort of tutorial option to help people out the first couple of days, and although there aren't any gates for water to interact with I have to add to everyone here that trapdoors theoretically already exist, however it requires a block of TNT to be placed a block into a hole and a sand block over that, topped with a pressure plate; the plate causes the TNT to drop down into the pit and the gravity effects of sand make the victim fall with it, ending with a delightfully cynical explosion somewhere during the drop which I personally think is much better than a simple trap door (although I still want to banish people to a Creeper Pit, but I must say this proves how many neat unintentional contraptions people can create along with catapults and minecart boosters)
As someone previously said, 4-8 lapis shards now drop from lapis lazuli blocks but not in SMP, but regardless of this it's still too difficult for making simple blue wool blocks. On a related note, Zombies drop feathers because at that point there were no chickens and he couldn't think of anything at the time
I also agree with some sort of metal detector, however it might be added as some sort of spell or something if the rumor Notch plans to use gold to enhance magical abilities is true
Personally, I'm hoping they add fossils and more weaponry, maybe a ball and chain that you swing over your head, hurting anything within a one block radius (even behind you) I've also seen a lot of good mods adding items like winged sandals that get rid of fall damage, elemental arrows and even mob-controlling rods as well as creatures like werewolves, ogres and lions, I really hope Notch makes those official in some way