So I've had my R4DS almost 2 weeks, played a ton of different ROMs, got 100% in CatlevaniaOR and have had no issues with any ROMs whatsoever. No long black loading screens on Animal Crossing either. On 2 occasions My DS did not recognize my R4 on power-up so I turned it off, ejected/reinserted the card and it worked fine. I have a plain Sandisk 2GB microSD (not an Ultra II) card formatted to FAT32 via Windows. I haven't tried download play, so I can't attest to it working or not but ROM play has been perfect.