ext2load usb 0:1 0x8000000 /boot/uImage.sheeva.20090319
No, it is correct. 0:1 specifies usb device:partition. 0x8000000 is the write address to memory for the image (you later bootm from this same address since it is were you wrote the kernel with ext2load). /boot/uImage.sheeva.20090319 is the image name with full path (the ext2 file system on the disk provides the actual disk read address and size of this file for reading).
The NAND doesn't have a partition table (this is why we have to pass it to the kernel by including the mtdparts in the bootargs section of the uboot bootcmd we use) We must also tell uboot the starting address to use for reading the kernel from flash and the length to read. The kernel image is usually written raw to the second partition of the flash. Again there are no real partitions, we decide how we want to divide it and then we must pass this information to uboot and to the kernel. Most of us are using the 1st 1MB of flash for uBoot, then the next 4MB of flash for kernel Image, and the rest for the root file system. Once you have picked the partition you intend to use you must be consistant with the information you pass to uBoot and the kernel. The reason some of the documentation uses different numbers is because some people divide their flash differently. You must adjust the commands to match the partitioning you are using.