Also posting from my 3DS, the web browser is very nice and fluid. I was able to get Excitebikes before the shop stopped working.
I have that on my Wii, among other games... Somethings tells me you must buy it again for the 3DS.

just put the sd in your computer and load songs onto it
Songs must have a certain audio format.
At least, on the DSi, it's extremely specific...