I recently upgraded two machines (one Debian testing, one Ubuntu 10.04) from grub-legacy to grub-pc. I've been using grub-legacy (aka GRUB) for many years, so I expected some surprises. My machines have a dedicated ext2 partition for /boot.
Problem number 1 - this message was displayed on boot, accompanied by activity on the empty floppy drive. But the machine booted OK. Just looked a bit worrying.
It's all down to insmod lvm to make GBUB2 lvm aware. I guess loading the module makes GRUB2 look on all drive-like devices to search for disks under lvm control, and someone decided to look on floppy drives as well.
Looking more closely, /etc/default/grub had the GRUB_TERMINAL line commented out, so GRUB2 decided to use a graphical terminal and so needed a font file from /usr - which is an lvm file system. Great, a boot loader that needs to access /usr! I uncommented the GRUB_TERMINAL=console line in /etc/default/grub and updated grub. I can cope without a graphical terminal, I no longer have insmod lvm in grub.cfg, and I no longer have the error.
One machine does have a W*nd*ws partition on it, but this wasn't found automatically by GRUB2. Turns out grub-common recommends the os-prober package, but I didn't have it installed. I installed os-prober, GRUB2 finds that partition and adds it to the menu.