I've noticed a sharp rise in MBR and boot sector rootkits, and now as part of a standard OS reload procedure use a Linux LiveCD to run DD and zero the first 4GB of a drive before reinstalling the OS.
But I will be surprised if they find a way to reliably infect the BIOS. BIOS code varies widely from system to system as it is the hardware specific level providing glue between chipset and OS. For such a thing to be possible, it would have to target similarities in a particular vendor, such as Phoenix.