I swapped my dead C2750 (Supermicro A1SAi-2750F) board for my cold-spare C3558 (A2SDi-4C-HLN4F) and was right back running again. I guess if you're talking about an appliance it's a little different, but this was just my home firewall/router FreeBSD+PF+Jails machine.

And actually a good reminder for me to eBay up another cold spare, because I totally forgot to.