Wireless technologies have been derided in the past for being unreliable as well as cheap and nasty.
They have improved immeasurably in the last few years and if certain criteria are respected then wireless technologies can provide excellent service.
Alarm systems. These are now very reliable, using signal encoding to eliminate false alarms and hacking, they are easy to install and can alert you to any incident using SMS or email.
Multi-room music. Wireless system which can do this include Sonos and Control4. While wired systems are certain to work all the time, wireless music systems will work most of the time and since they are non-critical systems anyway, the small inconvenience of losing music occasionally may be more than compensated by the lower cost of installation.
Wireless TV. Usually used for ad hoc connections which are only needed for a short time. TV and especially HDTV requires large bandwidth to be successful and wireless cannot always provide this. The technology is being developed by some high profile players and will one day be useful.
Wireless lighting. Lighting requires power and so cannot be totally wireless. There are systems which have dimmers and switches which can be added into existing wiring with minimum disruption. Control4, Rako, Lutron, Ulti, EnOcean and many more. The switches can be battery powered or mains powered. Some can be included in conventional UK wiring, and some can be put anywhere. Just look at the Schneider Electric Ulti range. You could even put a light switch in the middle of a pane of glass and it would operate perfectly and look really stylish.
The technologies vary widely. Some use zigbee mesh networks which are very robust if set up correctly and some use direct master to slave comms which can have issues with large distances or thick walls.
The real problem with wireless lighting is speed of response and consistency of speed of response. We are so used to a light coming on instantly when we press a switch that any delay causes consternation and doubt in the mind of the user. This can be frustrating and, in extreme cases, may eventually result in the system being rejected.
A wireless map should always be produced by the installer to show where any rf dead spots exist. In this way more certainty can be built into the design.
Wireless heating. There are some excellent new systems available now. Honeywell Evohome is a good example. Heatmiser also have a wireless range. These are excellent for retrofitting and provide advanced features such as web access to all heating zones and the ability to set up individual heating schemes for each room.
As with all wireless systems care is needed to ensure that there are no RF dead spots. In heating systems the wireless links can afford to tolerate some missing information since heating is necessarily a slow process, and provided the links reestablish themselves often enough then the missing information will be invisible to the user and temperature control will be acceptable.
I haven't covered all types of wireless technology, for example there are GSM based units which can control parts of your home technology, heating, lighting etc, but they are a slightly different ball game.
Wireless smart-home systems need care in designing and setting up but can provide excellent service and when being retrofitted can save lots of money. Beware also of having too many wireless systems concentrated in one house as many of them use the same frequency range and can interfere with one another.