I do a lot of photography and i have 9 SDHC cards, 6 of them are 8GB, 1 is 4GB and the remaining 2 are 2GB. Of them, my N800 reads only one of the two 2GB cards and not a single one of the remaining 8 (tried both slots). It also reads the ridiculously cheap 128 MB card that came with the device. All of my cards are branded (Sandisk, Kingston and Transcend), the cheapest one must be the 2GB card it actually reads - it's a PNY that was bundled as a gift with a graphics card I bought two years ago (an Nvidia Quadro).
Although I like the device too much, in fact all my posts are written on it, I don't trust it anymore. I guess I'll be bringing back to the shop after all.
Thanks to all people who posted here trying to help me.
Take care ;-)