Wherever possible go with a wired network over a wireless network - performance will be superior, more reliable, and more secure.
For me anyone building a new house is mad not to run at least several lengths of CAT 5e to every room – this gives you the option to have a network point in every room, but gives endless options as they can be used as for things like Windows Media Center Extenders (just brilliant), home automation, USB extenders etc. CAT 6 would be best for future proofing.
Running CAT 5 or 6 to each power socket and light switch will give you the option of installing a home automation system, though an X10 system might do the job for much less cash.
In short, wireless is great on paper and pretty good in practice, but nothing performs as well, or as cheaply, as a wired network.
That said, I also think anyone who pays the likes of smarthomes that kind of cash is also mad – you could install both a CAT 5/6 network (mine cost me about €300 including 300 metres of CAT 5e, and 50 RJ45 points and faceplates) and an X10 home automation system, which will work wonders for you if you can learn the skills to install and control it, for well under €2,000.
Installing a CAT 5e network really is as simple as buying the cable, running it from each room and back to a central point (called node zero in a spare room) before the walls are slabbed, then slab the walls and ceiling, and then cut out the holes for your faceplate and terminate the cables using a Krone punchdown tool to connect the cable to the RJ45 sockets – takes about a minute per cable, and maybe 5 minutes to cut out hole and fit the faceplate.
In half a day you’d run the cables yourself, and in another full day you’d fit all the faceplates and terminate the cables after the walls have been slabbed.