Hi!
I have received my micro sd today! After one month, now i can test my R4.
I have bought a Kingmax 2GB/x66 (high speed and made in taiwan). I have formated it in FAT32 and i have tested it and it works very well. I have tested Elite Beat Agents (works perfectly), Mario Kart, Diddy Kong Racing and it's excellent!
About Mario Kart, the wifi connection works perfectly even if i play with the hidden tracks! It's so funny! Now i can play Waluigi Pinball and Tic Toc online! So good!
This is for the good news but for the bad ones, i noticed, like a lot of people, that Tony Hawk DownHill as a variable rate (sometimes it's really speed but the most part of the time it's slow). And Castlevania PoR doesn't work at all. But i have trimmed the rom and maybe it was wrong... I will try later with the european rom.
So, in conclusion, the Kingmax seems to be a good card. For now it's the case, and i'll confirm it or not in the future.
Have fun with your R4 and DS!