There is. The first time you do at least a passable performance, you get a piece of heart, finishing the "pay back the chandelier" side-quest

I actually found that video too, as i started searching gamefaqs after i posted here, and "How do i do the minigame with Kina" was one of the most-answered FAQs on the Skyward Sword page

Glad to know it's not just me...

Oh right yeah.

I guess I forgot because I got it on my first try.

Anyway it's not worth worrying about too much, promise. Come back to it after doing some other stuff for a bit.

Oh no, i did it just now. Plenty of time still to go after some goddess cube chests...

^dang that was impressive playing... I played much more simply (though I don't recall the audience of two movement being as complicated as that) and still completed the task required.
(I also made each strum longer, but that's personal preference for the sound it makes, that video sounded rushed)

And yeah, no heart piece for the game... but you do need to do it to complete the Batreaux/gratitude sidequest.

Played a bit more last night.

One question though, was I supposed to give that letter to the toilet ghost hand or go find the actual girl he had intended it for? I did look for her, but gave up and just gave it to the toilet ghost hand.

EDIT: Just found out there are two solutions to this... and I think I chose my favorite option. However, I need to fully complete it next time I play by visiting Grooses room at night.

I also completed the chandelier side quest, got a few more gratitude bits, completed my first soul test, and I am about to go after the fire in the woods.

Lol at the new hand-in-the-toilet subquest.

I was also amused by the use of the sacred time gate to grow a plant. The train of logic is fairly subtle, yet also incredibly obvious.

Bloody hell, do I feel so left bhind. . .

Something's gone janky with my motion plus. Took me ten minutes to get through actually playing the song of the hero...

Well, spent a few more hours on it over last couple of days.

Acquired the 2nd flame, hookshot, bow/arrow, baby's rattle quest, toughened up Fledge, acquired at least one of every bug/treasure, obtained 15 heart containers, 47 gratitude crystals, can hold 1900 rupees, fully equipped adventure pouch, heart/treasure/cursed/rupee/extra heart/potion medals, ... I think that's it for now.

Have you guys upgraded any equipment? I upgraded all my shields (wood/iron/sacred) to the 2nd level, bug net (2nd), beetle (speed only), bomb bag (med), quiver (med)... I am thinking of upgrading beetle for endurance, sacred shield to max, and bow to iron next... especially since I am now about to head back to the volcano and its currently wood.

Right now I'm going to the fourth dungeon (I guess), where Groose follows Link and meets Hyrule for the first time

I've been playing 27 hours so far, having so much fun, GOTY without a doubt