Actually, with quite a bit of ingenuity, and help from my good friend Cris, I've largely managed to get Cat5, aerial cable and other stuff round under carpets, in hollow skirting boards and other trunking. The other problem was that Wi-Fi wouldn't get through the walls, so the network had to be Cat5.
As well as for the network, Cat5 is used to remotely control the kitchen computer, which is well away from the fumes and possibility spillage accidents in a large hall cupboard (Thanks,Tahir), Cat5 is also used for a Milestone AV Sender from one end of the house to the other.