I am currently working on completing Skyward Sword 100%. However, I'm going all out for this one. I've completed Hero Mode, got the Hylian Shield, completed every side quest, found every Gratitude Crystal, gotten every upgrade possible, found every Adventure Pouch item, every Piece of Heart, and now I'm working on the final step: getting my collection screen full to capacity.
What I mean by that is I'm attempting to get 99 of every single bug and treasure in the game. I will not consider the game 100% complete until I've achieved that, too. My progress so far is as such:
Deku Hornet: 99
Blessed Butterfly: 99
Gerudo Dragonfly: 38
Starry Firefly: 99
Woodland Rhino Beetle: 72
Volcanic Ladybug: 99
Sand Cicada: 53
Sky Stag Beetle: 52
Faron Grasshoper: 73
Skyloft Mantis: 99
Lanaryu Ant: 99
Eldin Roller: 99
Hornet Larvae: 29
Bird Feather: 99
Tumbleweed: 99
Lizard Tail: 47
Eldin Ore: 57
Ancient Flower: 33
Amber Relic: 99
Dusk Relic: 6
Jelly Blob: 99
Monster Claw: 39
Monster Horn: 99
Ornamental Skull: 29
Evil Crystal: 19
Blue Bird Feather: 34
Golden Skull: 16
Goddess Plume: 66
It's a long road, but it's a lot of fun and it gives me something to do. I'm just thankful for the Moonlight Merchant; otherwise I wouldn't be able to get so many Goddess Plumes. He's great for getting the three rare treasures. I don't think I could do this without that guy.
... I feel like I'm going a little overboard on this 100% thing, though. And by god I have way too much free time on my hands.