So, I checked everything over.
I forgot to mention that when I first got it back, I was silly to have started the StreetPass Mii Plaza right away to see the five new StreetPass tags before inserting my own SD card! Oops! So I powered off, and stuck my card back in, but then, though the five people my original 3DS passed were in my Plaza, I didn't have a chance to get puzzle pieces from them or use them in Find Mii II! >_< I didn't think the SD card was required, but it gave me some message about that... Luckily when I went back in after isnerting my card, I got the "Special" Reggie Mii released that day for the one-year anniversary and at least got one more Kid Icarus: Uprising pink piece, and noticed he was already at Level 5. (I guess if I do go to E3 this year and StreetPass, say, Miyamoto, I'll be able to tell if he's the real deal if it's sparkly like Reggie's Special Mii is.)
About those five Miis...one was from Alberta a day after I brought my 3DS to Purolator, and then two days later, four were from British Columbia (where Nintendo Of Canada resides), and I know at least one is of a NoC employee because its name is "Elder", the same name of the person who signed for my package according to the Purolator web site.
Should I be honoured that I'm Elder's 1001st StreetPass tag? I didn't get any StreetPasses on the way back because the new 3DS was off when they sent it, though fully charged when I turned it on.
The time and date were wrong, no biggie. I had to re-select my region when I went into either the System Settings or the eShop, don't remember which. Speaking of the eShop, I noticed my amount of funds were retained, phew!
I noticed a blank in my menu when there wasn't one before. I looked at my list of previously downloaded games, which was still at 50 (sounds like a lot, but not really, considering that includes the 3DS Ambassador games and all the free preview videos and demos) and found that it was the DSi game, Photo Dojo. I redownloaded it, and though I know the save file is separate, I started it up just to be sure my created characters were still there, and they indeed were. I don't know why it had to be redownloaded while Shantae: Risky's Revenge (another DSiWare game) didn't have to be, but no big deal.
And I can still edit my Miis (unlike on the replacement Wii I got, where I couldn't edit the Miis created on the original).
So if you send in your 3DS to be fixed, but it ends up being replaced, you shoudn't have to worry about Coins/eShop funds/downloads/saved games/Miis/etc. But there is a box you have to check off on Nintendo's web site with their disclaimer that sometimes data can't always be retained, depending on damage, so I guess they're covering their butts, particularly if your 3DS (or other unit) are damaged in some particular way.
Thumbs up, Nintendo. Thanks for doing this quickly! I love my new 3DS!...though if I had known for sure that they were going to replace it, maybe I should have asked for a Flame Red one instead... >_> I suppose if/when my brother wants one, maybe I'll give him this black one, buy a Flame Red one, and use the System Transfer function...
I do agree that the "replace-instead-of-repair" mentality is a good idea in the sense that it gets rid of the problem by simply replacing the whole unit, but hopefully they do something useful with the old one like reuse its good parts, and melt down or otherwise recycle the bad parts into materials.
(On an unrelated note, I got the last puzzle piece yesterday! I now have all the puzzles completed! Bwahaha! Now to get the remaining hats...)