I used to chainload from/to MBR & PBR as I used a grub only partition for booting. I did not originally like grub2 as it did not like to be installed to a partition. But now that I understand grub2 I consider it much better.
One issue can be that your boot drive will always be hd0. So you cannot copy a chainload entry from one to another drive without editing it, or sometimes you just have to edit the grub entry as you boot to get the correct drive number.
These are all entries from my old grub legacy that worked. I had three drives and often booted sdc, these entries now look like I was booting sda.
title Ubuntu 9.04 Jaunty 64 bit @ sdc5
title Most Current Ubuntu on sdc5
kernel /vmlinuz root=/dev/sdc5 ro quiet splash
title Ubuntu 9.04 Jaunty 32 bit @ sdb
title Ubuntu 9.10 Karmic 64 bit @ sdc
title Ubuntu 10.04 Lucid alpha/beta @ sda