GtW,
Fine to use wired ethernet if you have either flood wired your dwelling - like they do in new domestic buildings in Scandinavia and Germany, apparently - or don't mind trailing wires around the house.
Not so convenient if you wish to occasionally work with a lappy in the garden, in bed, or on the kitchen table.
Or if someone visits, or if the sprogs need to play games with their friends, or if you want to use a PDA with wifi etc.
WiFi is here to stay, better to know how to maximise the benefits and minimise the risks.
SD