Considering building a computer (as long as all the parts are delivered on time) takes about an hour to do, building one for friends and family isn't a major headache.
Its when FRIENDS of friends and family start asking me to build PCs, it starts to get annoying. I usually say "yeah ok, the parts will cost £xxx so I'll charge you an extra £xxx for the time" If they still want it, ok I made a little cash, if not, I've just saved myself and hour and a lot of after sales support (why doesn't my mouse fit in the PS2 slot??.....because it's USB.....Oh..Ok)
Still I enjoy building PC and when I look at what Dell, Sony, Packard Bell etc are selling, it makes it worth while when I look at the machine I'm building (or one's I've build already) and see that, for the money, it will blow any of their machines out of the water.