Wookey: Hope this isn't too stale now, missed it when it was posted. I used Rehau skirting trunking in my new extension.
I used pvc conduit up to the back boxes. It was a great success and I can access all the wiring at will now. I couldn't find a distributor for the parts so had to buy them from the manufacturer, who only sold in tens, but they gave me 40% discount without any difficulty. We have all the usual extra services in them, although I haven't got as far as 1-wire yet.
I liked this approach as it is visually no different from wooden trunking (see picture at the bottom).
However in the new conservatory we have red brick walls which I didn't want to spoil, so there I used Starline trunking:

Not quite as discrete but very flexible if you want to move sockets around or add them.