I would recommend doing it, i plan to wire my two bed apt to Cat5 why, because Wireless is fine as along as you and your neighbours use a differant channel on it, there are only three completly seperate ones, so if next do puts there wireless on the same as your it will cause conflict, second security. Wireless does not have enough bandwidth for HD Streaming etc, if you ever get to the stage where you want to transfare a file over wireless that is anyway large so 600mbps then be prepared to wait.
Next, all Games consols now have Ethernet (Wired Network), You can distribute your phone by it and your basically future proofing your home, i have two games consoles and two pcs and a wireless acccess point, at home, all share the same files off a Network Harddrive, meaning i don't need to have anyone thing on all the time to get my music etc....
I am an IT Tech but now a days these sort of things are becomming more and more common.
And while the walls are being done put in the cables, although i would say at least you would want one point for each wall point, the coax idea above is also very good.
I use an Apple Airport extreme base station also available now is a Time Capsule (basically a Wireless access point with a hard drive in it)
I am doing up the house completely. I have a sat dish with a quatro LNB into a loftbox which combines this with cable and FM (when rte finally goes out of test)
I do this so I can run a single coaxial cable to any of the points in the house and use a triplex switch that separates it all back out again. My Cable modem and router are in the attic.
I am only going to run cat5e Shielded from the attic to a 4 rj45 plate at socket level behind the back of the tv. The coaxial will run to each sitting room, bedroom and to the kitchen.
A dual coaxial cable is run down to the main sitting room. This is for Sky+ type viewing. (you need two cables, one for each tunner for Sky+ (PVR))
I am chaising wire around the sitting room and putting a faceplate behind the back of the tv for the surround sound system as I don't like unsightly wires.
As I have equipment in my attic and dont know what may happen in the future I am running a 2 x 4 inch duct from close to floor height to the attic from the back of the tv unit should I need to run wires like that in the future.
For the phone. Its in the attic. Wireless 2nd ary base stations can be set up around the house without the need for further wires.
As skyboxes need a phone line then I also have a phone outlet at the back of the tv sheilded connected to the attic.
There is no reason to run cat5 around your complete house but it does make sence to run it on where you will need it. In my case attic to sitting room.
maybe in your case study to attic also. Making use of your attic for the technology clutter can be a good idea.
For me its an only option. as for hdmi. There is 0 reason to do this. you never want to lay hdmi cable around your house. I was thinking you could have you sky box in the attic etc. but the signal de grates with such lengths unless you live in a bungalow that is. The same with scart, not a good idea.
With 1080p + you want short cables for this HDMI under 2m. You can't get a 25 ft cable to do the PS3 full throughput for example.
As a final note bear in mind that if you are running cable then go for shielded and get it done by a professional. I know what I am talking about but I still got a professional to do the work. Why ? cause if I layed the wrong cable then it would mean uprooting the wall.
If you play on putting a surround sound system in then do the cabling now. 5.1 is enough
If your running cable then buy wallplates.
As for wireless. I use 802.11n a lot faster and as most people are on 802.11b/g I don't have any issues with interference or speed.
http://en.wikipedia.org/wiki/IEEE_802.11
3+ times faster. longer range and not many people using it yet.