At least mine doesn't: Code: imac:~ MPE$ sudo ifconfig en0 mtu 9000 ifconfig: ioctl (set mtu): Invalid argument
Yes, the 27" does. Weird. My 27" 3.1GHz iMac that was delivered yesterday supports jumbo frames fine. I was quite concerned that it wouldn't because I rely on them for good performance with my NAS I set it using System Preferences -> Ethernet -> Advanced -> Ethernet -> Configure Manually. I've confirmed the setting by checking the output of ifconfig. It shows an mtu value of 9000. Paul