Might be worth reading http://www.coreboot.org/Board:lenovo/x60 - seems like there's still some rough edges on the BIOS replacement.
The T61 which is where my main experience lies has hardware whitelists for WiFi cards and restricts the internal SATA port to basic SATA speeds rather than SATA2 speeds which the chipset supports.
There are many hacked BIOSes (I use Middleton's BIOS) out there which fix this though.
On my X1, it's impossible to boot from the SD card reader and only the official ($$$) USB Ethernet adapter will allow PXE-boot.