I just installed two little surge protectors on the Ethernet lines going to two PCs. One of these PCs recently had the motherboard replaced because it's network port had gone out immediatly following a thunderstorm and, unfortunately, was integrated. Luckily, the system was under warranty and didn't cost the customer anything other than inconvenience. If this were to have happened outside of warranty, they would have been charged for a replacement motherboard as well as technician time to replace the part (eg. $200-$300).

APC PTEL2 2-line Telephone Surge Protector