[Francois_C]

The 30,000 eBooks limit is exactly the sort of commercial lie I hate; this figure has been calculated this way: a 32 Mb SD-card can contain 32 MB, that is nearly 30,000 x 1 Mb e-book files!
But the Kobo is absolutely unable to parse as many files, and it has no room for as many books: for any book cover, it creates monochrome copies of the cover that often need about 200 KB for each book in the /.kobo/pictures/ directory. For 30,000 books the Kobo would need 6,000,000,000 bytes of main memory (6 GB). Mine has only 1,434,600 bytes. This is false advertising by unskilled merchants.
As for me, I tried with up to 800 books on a 4 GB SDHC. As I don't care about brands I could not tell which, but this is an ordinary one. The Kobo is slow, but, well, it works. I already reduced to 700, and I plan to erase the complete Proust, Balzac and so on, because I loaded them hoping that the Kobo would allow fast searches as other handheld devices, but it is the slowest of all slow devices I ever owned. Really prehistoric to my mind...
I often save compressed archives of the contents of both Kobo and SD card. Each one is nearly 250 Mb. When I have a problem, I restore from the two files of the same date, which also defragments the flash memories.
One thing I noticed too: if you format the SD card through the Kobo cord (when it is plugged to the Kobo), the card will no longer be recognized by the Kobo, till it is formatted separately. (I use SDFormatter). The card must be formatted through a SD adapter directly connected to the computer. I noticed that a user in another thread could only format the card with his Blackberry. Maybe he tried to format the card while it is plugged to the Kobo. Though I know it it still happens to me...