I am quite "happy" to see that others have this issue too, I was a bit afraid that my NAND is slowly start to dying.
root@sagan:~# dmesg | grep "I/O error"
[ 14.043712] print_req_error: I/O error, dev mtdblock0, sector 0
[ 14.063686] print_req_error: I/O error, dev mtdblock0, sector 8
[ 14.064133] print_req_error: I/O error, dev mtdblock0, sector 16
[ 14.068792] print_req_error: I/O error, dev mtdblock0, sector 24
[ 14.075148] print_req_error: I/O error, dev mtdblock0, sector 0
[ 14.080641] Buffer I/O error on dev mtdblock0, logical block 0, async page read
[ 14.185514] print_req_error: I/O error, dev mtdblock0, sector 0
[ 14.185550] Buffer I/O error on dev mtdblock0, logical block 0, async page read
[ 14.190944] print_req_error: I/O error, dev mtdblock1, sector 0
[ 14.198236] print_req_error: I/O error, dev mtdblock1, sector 8
[ 14.204103] print_req_error: I/O error, dev mtdblock1, sector 16
[ 14.209922] print_req_error: I/O error, dev mtdblock1, sector 24
[ 14.216309] Buffer I/O error on dev mtdblock1, logical block 0, async page read
[ 14.223953] Buffer I/O error on dev mtdblock1, logical block 0, async page read
[ 14.994921] Buffer I/O error on dev mtdblock0, logical block 0, async page read
[ 15.000224] Buffer I/O error on dev mtdblock0, logical block 0, async page read
[ 15.007452] Buffer I/O error on dev mtdblock1, logical block 0, async page read
[ 15.014787] Buffer I/O error on dev mtdblock1, logical block 0, async page read
[ 41.086892] print_req_error: I/O error, dev mtdblock0, sector 0
[ 41.099466] print_req_error: I/O error, dev mtdblock0, sector 8
[ 41.099894] print_req_error: I/O error, dev mtdblock0, sector 16
[ 41.104642] print_req_error: I/O error, dev mtdblock0, sector 24
[ 41.132680] print_req_error: I/O error, dev mtdblock0, sector 0
[ 41.132704] Buffer I/O error on dev mtdblock0, logical block 0, async page read
[ 41.148892] print_req_error: I/O error, dev mtdblock0, sector 0
[ 41.148917] Buffer I/O error on dev mtdblock0, logical block 0, async page read
[ 41.174308] print_req_error: I/O error, dev mtdblock1, sector 0
[ 41.174715] print_req_error: I/O error, dev mtdblock1, sector 8
[ 41.179435] print_req_error: I/O error, dev mtdblock1, sector 16
[ 41.185391] print_req_error: I/O error, dev mtdblock1, sector 24
[ 41.196486] Buffer I/O error on dev mtdblock1, logical block 0, async page read
[ 41.199496] Buffer I/O error on dev mtdblock1, logical block 0, async page read