Just my $.02,

I have not (so far!) had any problems. I have had my N800 for about 10 days. As soon as I got it, I flashed the July 7 release. I purchased 2 Kingston 4GB SDHC cards when I got the N800. Both are installed. I have used the USB to copy a couple of CD's worth of MP3's as well as some videos, to the External MMC. I have Maemo Mapper configured to save maps to the internal MMC.

Hopefully, I have not jinxed myself by writing this...